Updated September 2026. A custom online store is built around the way your business sells. That is its biggest strength, and it is also why planning matters more than on a template platform: every rule has to be written down before it can be built. This is the checklist we work through with clients before we design or code a custom ecommerce website, in the order we would tackle it.
The short version
- Write a one-page brief with goals, must-haves and constraints.
- Check that you need a custom build at all.
- Scope the catalogue, stock, pricing and orders.
- Plan payments, VAT and the checkout.
- Write down your shipping and fulfilment rules.
- List every integration and decide which system owns which data.
- Start product data, copy and photography early.
- Plan SEO and, if you are replacing a store, the URL migration.
- Agree the architecture, hosting and security basics.
- Set a realistic timeline and budget, and phase what can wait.
1. Write a one-page brief
Before anyone talks about technology, get these on one page:
- What you sell and to whom: consumers, trade customers or both, and whether you ship in the UK only, to Europe or worldwide.
- Goals for the first year, in numbers you will actually track, such as orders per month, average order value or the share of sales from trade accounts.
- Must-haves for launch, and a separate list of things that can come later.
- Constraints: budget range, deadline and any fixed dates such as a product launch or your peak season.
- People: who makes decisions, and who will run the store day to day.
2. Check that you need custom at all
If your products, prices and delivery rules are standard, a hosted platform may serve you better and cost less. A custom build makes sense when your pricing, wholesale terms, checkout or integrations don't fit a template, or when the shop is one part of a bigger platform. Our Shopify vs custom e-commerce comparison sets out the real costs of both routes and a checklist of signs that you have outgrown a platform.
3. Scope the catalogue, stock, pricing and orders
This is the heart of your e-commerce scope of work. Answer these questions in writing:
| Area | Questions to answer |
|---|---|
| Products | How many products? Which options create separate variants with their own stock (size, colour), and which are add-ons (engraving, gift wrap)? |
| Stock | Where does the true stock figure live? One location or several? Do bundles take stock from their individual items? |
| Pricing | Retail only, or trade and volume prices too? Are any prices calculated from measurements or materials? How do discounts and codes combine? |
| Customers | Guest checkout, accounts or both? Do trade accounts need approval? |
| Orders | What happens after payment: picking, dispatch emails, part-shipments, returns and refunds? |
For every unusual rule, write out one real example order from start to finish. Examples catch edge cases that bullet points miss, and they become test cases later.
4. Plan payments, VAT and the checkout
Payments
We usually integrate Stripe, which handles cards, Apple Pay and Google Pay, and can add PayPal alongside it. Stripe's UK pricing in September 2026 is 1.5% + 20p for standard UK cards, 2.8% + 20p for premium UK cards, 2.5% + 20p for European cards and 3.15% + 20p for other international cards, plus 2% if a currency conversion is needed. Using Stripe's hosted payment fields means card numbers never touch your server, which keeps your PCI DSS obligations light, and Stripe handles the Strong Customer Authentication checks that UK card payments require.
VAT
- You must register for VAT once your taxable turnover goes over £90,000 in a rolling 12 months, or if you expect it to within the next 30 days.
- Prices shown to consumers must include VAT. Trade customers often expect prices excluding VAT, so decide how each customer type sees prices.
- Record the VAT rate for each product. Most goods are standard-rated at 20%, but some are reduced-rated at 5% or zero-rated, such as books and children's clothing.
- Selling to consumers in the EU brings extra VAT and customs rules, and Northern Ireland has its own arrangements. Agree the approach with your accountant, and we will build what they specify.
Checkout
Offer guest checkout, show the full price including delivery before payment, and keep the number of steps low. Most online orders from consumers can be cancelled within 14 days under the Consumer Contracts Regulations, so plan how returns and refunds will work in the admin, not just on the returns page.
5. Write down your shipping and fulfilment rules
Delivery rules are easy to underestimate. List your zones (for example UK mainland, Highlands and Islands, Northern Ireland, Europe, rest of the world), how you charge (flat rate, by weight, by order value), free delivery thresholds, dispatch cut-off times and any click and collect option. Make sure every product has a weight and, if couriers charge by size, dimensions. If you print labels through a courier, the store can pass orders to the courier automatically instead of someone retyping addresses.
6. List every integration and decide which system owns which data
Typical integrations include accounting software (such as Xero or QuickBooks), stock or warehouse systems, email marketing, reviews, analytics and marketplaces. For each type of data, decide which system is the source of truth and how often the others update:
- Stock: the store, or your warehouse system?
- Prices and products: the store admin, or a spreadsheet or supplier feed?
- Orders and invoices: created in the store and pushed to accounting, or the other way round?
Getting this wrong is how businesses end up selling items they don't have. We have built accounting integrations before, such as the Xero connection in Tenancy Pilot, a property management platform, and the same principle applies to any store: one system owns each piece of data.
7. Start product data, copy and photography early
Product data is the part of an e-commerce project that is easiest to leave late. Agree a spreadsheet template early (names, variants, prices, weights, attributes for filtering, descriptions and image file names) and start filling it while the site is being designed. Write your own product and category descriptions rather than copying the manufacturer's, and shoot photos with consistent sizes and backgrounds. Serve them in a modern format: our tests on which image format to use for product photos found AVIF files 37% to 67% smaller than JPEG at the same visual quality.
8. Plan SEO and the URL migration
If you are replacing an existing store, a migration plan protects the rankings you already have:
- Export every URL that gets search traffic from Google Search Console, and crawl the old site for the rest.
- Map each old URL to its new address, and set up 301 redirects before launch.
- Carry over page titles, descriptions and product and category copy that already rank.
- Add product structured data (price, availability and reviews where you have them) and an XML sitemap.
- After launch, submit the sitemap and check Search Console for errors every week for the first month or two.
For a new store, plan your categories around the words customers actually search for, and give every category page a short, useful introduction.
9. Agree the architecture, hosting and security basics
For custom e-commerce architecture we use Django and PostgreSQL, with background tasks (Celery and Redis) for emails, image processing and data syncs, hosted on cloud platforms such as AWS, Render or DigitalOcean. Whoever builds your store, agree these basics up front:
- A staging site where you can test changes before they go live.
- Automated, off-site database backups and version control for all code.
- Uptime and error monitoring, and a plan for security updates.
- Admin accounts with the right permissions for each member of staff.
- Load testing if you expect traffic spikes from drops, sales or press coverage.
- Ownership: the code, domain, hosting and payment accounts should be in your business's name.
10. Set a realistic timeline and budget
Timeline
A custom store goes through discovery and scoping, design, build, content and data loading, testing and launch. We build in weekly sprints and show you progress at the end of each one, so problems surface early. After launch we monitor the site closely for the first 48 hours, and bugs found in the first 30 days are fixed at no extra cost. What makes a timeline longer is predictable: more integrations, complex pricing rules, messy data to migrate, product content that arrives late and slow decisions.
Budget
Our published starting points are around £2,000 to £5,000 for simple business sites, £5,000 to £15,000 for moderate web applications and £15,000 and up for complex systems. An online store with a checkout, stock control and an admin is a web application, so where yours lands depends on:
- How complex your pricing, discounts and wholesale rules are.
- The number and difficulty of integrations.
- How much data needs migrating and how clean it is.
- How much custom design the product pages and checkout need.
- Whether we write content and prepare product data, or you do.
Budget for running costs too: hosting, maintenance, payment fees and any paid services such as email delivery. The best way to control cost is to phase it. Launch with the must-haves, learn from real orders, then build the rest.
Bring this to your first call
You don't need every answer before you talk to a developer, but the brief, your example orders and a first draft of the product spreadsheet will make the first conversation far more useful. When you are ready, book a free 30-minute planning call, or read more about our custom ecommerce website development service.