The verdict in three sentences
A Lyon property developer delivering 600 homes a year and receiving 2,500 buyer calls can absorb more than half of them with an extranet showing construction progress, stage payment calls under French off-plan (VEFA) rules and option choices. Kolonell builds this kind of custom application for 2.5 to 15M+ FCFA (3,810 to 22,870+ EUR) depending on complexity, with hosting and connectors quoted separately. Plan 4 to 6 months, with a pilot on a single development before rolling out.
Where the 2,500 calls come from
An off-plan buyer waits 18 to 30 months between signing at the notary and getting the keys. Meanwhile, they pay without seeing anything, so they call. Call analysis at a developer of this size nearly always shows the same split: half about progress and handover date, a quarter about payment calls, the rest about options, buyer modifications and documents.
| Call reason | Estimated share | Answer in the extranet |
|---|---|---|
| How is the site progressing, is the handover date holding? | 40% | Progress timeline and monthly photos per building |
| Payment call received, amount, due date | 22% | Personal schedule, downloadable architect certificate |
| Option choices (tiles, kitchen, sockets) | 15% | Options catalogue with deadline and online signature |
| Buyer-requested modifications | 8% | Online request, quote, electronic approval |
| Documents (contract, plans, specifications) | 10% | Document vault per unit |
| Handover preparation | 5% | Appointment booking, snagging checklist |
Off-plan payment calls: framing the legal schedule
French housing law caps payments by progress: 35% when foundations are complete, 70% when the building is weathertight, 95% on completion, the balance at handover, possibly held in escrow if there are snags. Within those caps, each developer sets its own contractual schedule. The extranet must show, for each unit, the stage reached, the architect's certificate, the amount called, total paid and balance due, then notify the buyer and their bank when it funds the mortgage.
| Stage | Legal cumulative cap | Supporting document | Notification |
|---|---|---|---|
| Signing of the deed | Based on deposit paid | Notarial deed | Welcome email and extranet access |
| Foundations complete | 35% | Architect certificate | Buyer and bank |
| Weathertight | 70% | Architect certificate, photos | Buyer and bank |
| Building complete | 95% | Completion certificate | Buyer, bank, pre-handover invitation |
| Handover | 100% | Handover report | Balance, or escrow if snags |
Intermediate stages specific to your standard contract (ground slab, partitions and so on) are added without extra development.
Options, buyer modifications and e-signature
Option choices are often handled by email and paper, with deadlines buyers discover too late. In the extranet, each unit shows its options catalogue, prices and the cut-off date set by the site team. The buyer builds their selection, receives the amendment and signs it electronically. Buyer modifications follow the same flow with a costing step by the technical department. Approved choices go straight to finishing trades as a sheet per home.
| Kolonell application level | Budget | Typical scope | Timeline |
|---|---|---|---|
| Simple | 2,500,000 to 4,000,000 FCFA (3,810 to 6,100 EUR) | Progress, photos, documents | 4 months |
| Medium | 4,000,000 to 7,000,000 FCFA (6,100 to 10,670 EUR) | Simple plus payment schedule and notifications | 4 to 5 months |
| Complex | 7,000,000 to 15,000,000+ FCFA (10,670 to 22,870+ EUR) | Medium plus options, modifications, e-signature, ERP connector | 5 to 6 months |
| Maintenance | 35,000 / 75,000 / 120,000 FCFA per month (53 / 114 / 183 EUR) | Fixes, improvements, monitoring | Monthly |
Mini case study
Thomas Garnier, head of customer relations, measures an average of 12 minutes per call, file lookup included. 2,500 calls equal 500 hours a year. If the extranet avoids 55% of them, the team recovers 275 hours, about 12,400 EUR a year at a loaded rate of 45 EUR per hour.
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The clearest gain comes from options. Across 600 homes, 30% of buyers take options worth 2,500 EUR on average, i.e. 450,000 EUR. A visible deadline and an online catalogue often lift that by at least 10%: 45,000 EUR of extra revenue a year. With a complex application at 18,000 EUR and maintenance at 183 EUR per month, the investment is covered in year one.
FAQ
Does the extranet connect to our development management software?
Yes, through an API or a scheduled export depending on your tool. The connector is quoted separately and usually adds 3 to 5 weeks to the plan.
Can buyers' banks access the certificates?
The buyer can share a secure link valid for 30 days with their bank adviser. This removes most follow-ups related to fund releases.
Who publishes the site photos?
The site manager, from a phone, once a month per building. Publishing takes under 10 minutes with sorting by unit.
Is the e-signature legally binding?
Yes, with a provider compliant with the EU eIDAS regulation, at advanced level for option amendments. Cost per signature is around 1 to 3 EUR in 2026.
Can we start with a single development?
That is recommended: a 2-month pilot on 60 to 80 units lets you adjust wording and notifications before opening every development.
Let's scope your project. Tell us how many developments are under way, your current tools and the pilot development you have in mind. 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.
