Websites11 min read

Writing a custom SaaS specification document in London: guide and cost (2026)

Mohamed Bah·Fondateur, Kolonell
September 15, 2026
Share:
Writing a custom SaaS specification document in London: guide and cost (2026)

Writing a custom SaaS specification document in London: guide and cost (2026)

Websites

The verdict in three sentences

A clear specification document is the best investment before building a SaaS platform: a framing workshop costs 4,000 to 12,000 EUR and takes 2 to 4 weeks. Without it, the gap between agency quotes commonly reaches 2x to 3x, not because agencies cheat but because they price different scopes. A good spec turns a subjective tender into an objective comparison.

The standard SaaS specification outline

A usable spec covers five blocks. Here is the expected content and relative weight.

SectionExpected contentWeightCommon trap
Context & goalsProblem, target, KPIs10%Staying too vague
FunctionalUser stories, journeys, roles40%Forgetting edge cases
TechnicalArchitecture, integrations, volume20%Imposing a tech for no reason
Security & complianceGDPR, auth, RBAC15%Treating it as an annex
Support & runMaintenance, SLA, roadmap15%Ignoring post-delivery cost

The functional section is the core: badly written, it is what makes quotes diverge.

Choosing your agency: the criteria that matter

The cheapest is almost never the right one. Here is a 2026 weighting grid.

CriterionWeightWhat to check
Similar SaaS experience25%References, live demos
Quality of proposed framing20%Reformulation of your need
Team actually assigned15%Seniority, turnover
Methodology & transparency15%Sprints, code access
Price and model15%Fixed price vs time & materials
Support & reversibility10%Code ownership, exit

Compare quotes on a common basis

Bring each quote to the same grid to avoid the sticker-price trap. Example across three offers for the same platform.

Need a professional website?

Kolonell builds websites that attract clients, optimized for the Sénégalese market. Free quote in 2 minutes.

Prefer a call back?

Leave your WhatsApp number and a Kolonell expert will get back to you within 1 business day. Free, no strings attached.

ItemAgency AAgency BAgency C
Framing6,000 EURincluded9,000 EUR
Development48,000 EUR95,000 EUR62,000 EUR
Scope covered60%100%85%
Year-1 support9,000 EUR14,000 EUR11,000 EUR
Code ownershipyesnoyes
Real cost at equal scope~90,000 EUR95,000 EUR~82,000 EUR

Quote A looks cheapest but covers only 60% of scope: at equal scope it converges with the others.

Mini case study

Julian, project director at a B2B software vendor in London, receives three quotes ranging from 48,000 to 95,000 EUR for the same platform. He invests 8,000 EUR in a 3-week framing workshop that produces a precise spec. Re-priced at equal scope, the three offers tighten to between 82,000 and 95,000 EUR: the gap drops from 2x to 15%. The spec spares him an estimated 30,000 EUR overrun on forgotten features and secures the agency choice.

FAQ

Should I pay for a specification document? A paid framing workshop (4,000 to 12,000 EUR) almost always pays off: it prevents incomparable quotes and overruns. Some agencies deduct it from development if you continue with them.

How long does framing take? Between 2 and 4 weeks for a medium-complexity SaaS platform, with 2 to 4 workshops, mockups and a delivered document. That is short against the 6 to 10 months of development it secures.

Why do quotes vary so much? Almost always because of a vague scope: each agency fills the gaps its own way. A 2x to 3x gap signals a poorly framed need, not dishonest agencies. The spec removes that gap.

What should the technical part contain? Target architecture, integrations, expected volume, performance and security requirements. Avoid imposing a specific tech without a business reason: let the agency propose and justify.

Should support be in the spec? Absolutely. Maintenance cost (10 to 20% of budget per year), SLAs and enhancements must be priced from the start, otherwise the quote comparison is skewed and the real budget underestimated.

Let's scope your project. Send us your goals and main features: we run a framing workshop and produce a comparable specification. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.

Tags:#cahier des charges#plateforme SaaS#appel offres#cadrage projet#comparaison devis 2026#methodologie#B2B
Share:

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.