The verdict in three sentences
For 700 employees, a booking SaaS at 2.50 to 7 GBP per user per month (about 3 to 8 EUR) costs 21,000 to 58,800 GBP a year, while a custom application integrated with Microsoft 365 and badge access control costs 45,000 to 110,000 GBP with a London agency in 2026 (market estimate), delivered in 10 to 14 weeks. The real gain does not come from the software but from measuring actual occupancy, which almost always reveals 30 to 40 % of desks and rooms going unused. In central London, that translates into thousands of square feet you can release, worth far more than the tool itself.
What a 700-person HQ app needs to handle
The facilities director manages three resource types with different rules: 40 meeting rooms from 4 to 30 seats, 12 pool cars with a logbook, and a hot desking estate. Native Microsoft 365 tools cover rooms, handle cars poorly and barely touch shared desks.
| Requirement (London, 2026) | Outlook and Microsoft 365 alone | Booking SaaS (market estimate) | Custom application |
|---|---|---|---|
| Room booking from Outlook and Teams | Yes | Yes | Yes, via Microsoft Graph |
| Automatic release on no-show | No | Yes, via sensors or check-in | Yes, tied to badge data |
| Hot desks by floor and team | No | Yes | Yes, with rules per department |
| Pool cars: licence checks, mileage, fuel | No | Rarely | Yes, digital logbook |
| Badge data for real occupancy | No | Connectors for some brands | Integration with your access control system |
| Neighbourhoods and team days | No | Yes | Yes, configured to your hybrid policy |
| UK GDPR data residency | Microsoft cloud | Vendor cloud | Your choice |
3-year cost: SaaS or custom
| 3-year item (2026 order of magnitude, GBP excl. VAT) | SaaS at 2.50 GBP/user | SaaS at 7 GBP/user | Custom app at 75,000 GBP |
|---|---|---|---|
| Setup and integrations | 5,000 | 10,000 | 75,000 |
| Annual subscription or hosting | 21,000 | 58,800 | 4,000 |
| Annual maintenance | Included | Included | 11,250 (15 % of build) |
| Room panels and check-in kiosks | 12,000 | 12,000 | 12,000 |
| Year 1 total | 38,000 | 80,800 | 102,250 |
| 3-year total | 80,000 | 198,400 | 132,750 |
| Ownership of code and data | No | No | Yes |
With London development rates, SaaS usually wins for a standard hybrid office. Custom earns its place when pool cars, badge integration and specific booking rules would otherwise require two or three separate tools.
Calculating real occupancy and releasable floor space
Booked occupancy almost always overstates reality: ghost recurring meetings, rooms blocked "just in case", desks assigned but empty. The method takes four steps:
- Measure for 6 to 8 weeks bookings, check-ins and badge entries by floor.
- Find the real peak, for example Tuesday and Thursday, not the average.
- Size the desk count to that peak, plus a 10 % buffer.
- Release or repurpose surplus space: sublet, hand back a floor at lease break, create collaboration areas.
| Measured indicator (example London HQ) | Before measurement | After 8 weeks of data |
|---|---|---|
| Desks | 500 | 360 needed (peak 325 + 10 %) |
| Average desk occupancy | Assumed 85 % | Actual 52 %, peak 65 % |
| Rooms booked but empty | Unknown | 28 % of slots |
| Space per desk, circulation included | 100 sq ft | 100 sq ft |
| Releasable space | 0 | 140 desks x 100 sq ft = 14,000 sq ft |
| All-in occupancy cost, Midtown | 95 GBP/sq ft/year | 1,330,000 GBP/year at stake |
Mini case study
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Sophie, facilities director of a 700-person headquarters in Midtown London, deploys a booking solution and runs 8 weeks of measurement. She finds a 65 % occupancy peak across 500 desks. She proposes to her board to sublet half a floor of 7,000 sq ft, recovering about 7,000 x 95 = 665,000 GBP a year in occupancy cost. Even the custom option, at 102,250 GBP in year one, pays back in under 2 months of savings; a SaaS at 38,000 GBP in year one pays back even faster. Automatic release of unattended rooms also cuts empty booked slots from 28 % to 9 %.
FAQ
How much does a custom room booking app cost in London?
As a 2026 market estimate, 45,000 to 110,000 GBP excluding VAT depending on resources and integrations. Microsoft 365 integration accounts for 8,000 to 15,000 GBP, badge access control integration 10,000 to 25,000 GBP depending on the manufacturer.
How long does it take to go live?
Plan 10 to 14 weeks: 2 weeks of scoping, 6 to 9 weeks of development and integration, then a 2 to 3 week pilot on one or two floors.
Can the app manage pool cars?
Yes: booking, driving licence validity checks, mileage and fuel logging on return. For 12 cars, this module adds 8,000 to 14,000 GBP to the project.
Does badge data raise compliance issues?
Under UK GDPR you need a documented purpose, a legitimate interest assessment, staff information and aggregation by floor rather than by person. Allow 1 to 2 weeks for legal work and configuration.
Do all rooms need panels?
No. Equip the 10 to 15 most requested rooms first, at about 400 to 700 GBP per panel, and use QR code check-in elsewhere.
Let's scope your project. We define with you the resources, Microsoft 365 and badge integrations and the occupancy measurement protocol before quoting. Detailed quote within 48 h. WhatsApp +221 77 596 93 33, or request your free quote.
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.
