The verdict in three sentences
For a London engineering consultancy of 20 to 80 people, a custom client extranet costs 40,000 to 70,000 GBP (about 46,000 to 81,000 EUR) and ships in 3 to 4 months. The payback comes mostly from lower email volume (around 45 % fewer) and traceable approvals, which protects you on variations and disputes. A customised SharePoint is cheaper upfront, but once you run drawing approval workflows, revisions and contractual milestones for clients outside Microsoft 365, custom usually wins within two to three years.
What an engineering extranet includes and what it costs
The typical scope has four blocks: a dashboard per project (RIBA stages 0 to 7), a document register with version control for drawings and calculations, a client approval workflow with timestamps, and messaging attached to each document. Figures below are 2026 estimates for a UK agency or a nearshore team managed from London.
| Module | Content | 2026 budget (GBP) |
|---|---|---|
| Core and authentication | SSO, MFA, roles for client, designer, contractor | 6,500 - 10,000 |
| Project dashboard | Milestones, progress by RIBA stage, delay alerts | 8,000 - 13,000 |
| Versioned document register | Revisions P01, P02, C01, comparison, watermark, logged downloads | 9,500 - 17,000 |
| Approval workflow | Status A, B, C codes, automatic reminders | 8,000 - 15,000 |
| Document messaging | Threads, mentions, email notifications | 4,000 - 8,000 |
| Integrations | Calendar, Excel export, link to internal project tool | 4,000 - 7,000 |
| Total MVP to full scope | 40,000 - 70,000 |
Add hosting and maintenance: 150 to 450 GBP per month on UK or EU cloud regions, plus an evolutive maintenance retainer of 500 to 1,100 GBP per month depending on request volume.
Custom, SharePoint or off-the-shelf: the comparison
Many firms start with shared folders. The real decision is between three options, compared over five years.
| Criterion | File sharing (Drive, Dropbox) | Customised SharePoint | Custom extranet |
|---|---|---|---|
| Upfront cost | 0 - 2,000 GBP | 18,000 - 35,000 GBP | 40,000 - 70,000 GBP |
| Annual cost (40 users) | 3,000 - 6,000 GBP | 9,000 - 16,000 GBP | 7,500 - 18,500 GBP |
| Native approval workflow | No | Partial (Power Automate) | Yes, mapped to your stages |
| Client experience | Poor | Average, Microsoft guest account needed | Simple, link plus MFA |
| Approval traceability | None | Fair | Complete, exportable for disputes |
| Time to deploy | 1 week | 6 - 10 weeks | 3 - 4 months |
The deciding factor is often adoption: many public and private clients refuse to manage yet another Microsoft guest identity. A custom build gives access through a secure link with two-factor authentication.
Security and hosting requirements
An engineering firm does not process health data, so no healthcare-grade hosting is needed. However, drawings of sensitive buildings, personal data of contacts and contractual commitments require UK or EU hosting compliant with UK GDPR. Plan for encryption at rest, access logs kept 12 months, daily backups with 30-day retention and Cyber Essentials Plus alignment, increasingly requested on public frameworks. A penetration test before go-live adds 5,000 to 10,000 GBP.
Mini case study
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Claire, managing partner of a 35-person structural engineering firm in Southwark, runs 25 projects a year. Each project generates about 300 emails with the client side, so 7,500 emails a year. At 4 minutes per email (reading, finding the right revision, replying), that is 500 hours a year. A 45 % reduction saves 225 hours, valued at 70 GBP loaded hourly cost: 15,750 GBP a year. Add one variation claim avoided thanks to traceable approvals (estimated 12,000 GBP over the year): total gain is about 27,750 GBP a year. For an extranet at 52,000 GBP with 10,000 GBP of annual running costs, payback comes in under 3 years, after which the net gain exceeds 17,000 GBP a year.
FAQ
What does a minimal client extranet cost for an engineering firm?
A first release with authentication, milestone dashboard and versioned document register starts around 40,000 GBP. The approval workflow and messaging can follow in a second phase of 12,000 to 20,000 GBP.
Is SharePoint good enough?
For internal teams already on Microsoft 365, a customised SharePoint at 18,000 to 35,000 GBP can work. It struggles when external clients must approve drawings without Microsoft accounts.
What is a realistic delivery time?
Plan 3 to 4 months: 3 weeks of scoping and mock-ups, 8 to 10 weeks of development, then 2 to 3 weeks of acceptance testing with 2 or 3 pilot clients.
Will clients actually use it?
Adoption depends on simplicity: link-plus-MFA access without account creation commonly reaches 70 to 85 % active use after 6 months. Making approvals possible only in the extranet speeds up adoption.
Can it connect to our project management software?
Yes, through an API or scheduled export, for 4,000 to 7,000 GBP depending on the tool. It removes double entry of milestones and timesheets.
Let's scope your project. Send us your stages, annual project count and security constraints, and we will price an extranet in phases, from 40,000 to 70,000 GBP, deliverable in 3 to 4 months. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
