The verdict in three sentences
A custom construction management platform for a London contractor costs between GBP 55,000 and 130,000 in 2026, versus GBP 40 to 100 per user per month for an off-the-shelf vertical tool. Custom becomes worthwhile above roughly 25 to 30 users, or when your applications for payment, site time capture and procurement fall outside standard workflows. Below that, a market product such as Procore or a mid-market UK tool ships faster and carries less risk.
What a custom site-management platform covers
The typical scope for a contractor covers estimating (quantity take-off), site programme, operative time capture, procurement and subcontracts, then valuation and applications for payment with retention. It is that estimate to valuation chain that justifies bespoke work: generalist suites handle cumulative monthly valuations and variations poorly.
| Module | 2026 scope | GBP range |
|---|---|---|
| Estimating and price library | Measures, items, prime cost | 9,000 - 20,000 |
| Programme and allocation | Gantt, resources, weather | 7,000 - 15,000 |
| Mobile site time capture | Offline field app, geo | 8,000 - 17,000 |
| Procurement and subcontracts | POs, receipt, final account | 7,000 - 16,000 |
| Valuations / applications | Cumulative, retention, variations | 10,000 - 22,000 |
| Reporting and job margin | Real-time dashboards | 6,000 - 13,000 |
Realistic delivery: 6 to 11 months for a full scope, with a partial go-live around month 4.
Custom vs vertical: the break-even point
The key calculation weighs the upfront custom build against the cumulative subscription cost of a vertical tool over four years. Treat these as 2026 order-of-magnitude figures, excluding training and data migration.
| Software seats | Vertical (GBP 70/user/mo) over 4 yrs | Custom (GBP 90,000 + GBP 700/mo support) over 4 yrs |
|---|---|---|
| 10 users | 33,600 | 123,600 |
| 25 users | 84,000 | 123,600 |
| 40 users | 134,400 | 123,600 |
| 60 users | 201,600 | 123,600 |
| 100 users | 336,000 | 123,600 |
The crossover sits around 28 to 32 users. Above it, custom wins and the gap widens fast: your subscription keeps climbing while support stays flat.
Need a professional website?
Kolonell builds websites that attract clients, optimized for the Sénégalese market. Free quote in 2 minutes.
Mini case study
Sarah is operations director of a groundworks contractor in London, 45 operatives and 6 site managers. She currently pays 51 seats at GBP 70/month, or GBP 42,840/year. A custom build at GBP 90,000 plus GBP 700/month works out to about GBP 38,400/year over three years, and falls to GBP 8,400/year once amortised. Mobile time capture also claws back roughly 3 hours per week of re-keying per manager: 18 hours weekly at GBP 32, over GBP 30,000/year of productive time handed back to sites.
FAQ
How long until first go-live? Expect 4 months for a first module (usually time capture or estimating) and 6 to 11 months for the full chain through to applications for payment.
Can we keep our existing accounting system? Yes. The platform connects to Sage, Xero or your ERP via export or API. Custom handles the site trade, accounting stays where it is.
What support budget should we plan? GBP 600 to 900 per month in 2026 covers fixes, minor evolutions and hosting. Major features are quoted separately.
Does custom handle retention and variations? Yes, and that is precisely where generalist suites fall short. A bespoke model computes cumulative valuation, 5% retention and variations with no re-keying.
At what size does it pay off? Around 28 users over four years. Below that, a market vertical remains the best cost/risk choice.
Let's scope your project. Tell us your headcount, contract types and where valuations hurt today, and we will frame a scope between GBP 55,000 and 130,000 by module. 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.
