Wertblick

Roof-coating companies clean existing tiles and give them a new coating. I knew people at one of these companies through friends, and that gave me the idea: a sales rep takes a photo of a house, picks a coating colour and shows the homeowners their own roof with the new finish.

Getting the roof right

Most of the work went into the prompt. I iterated and tried out what works and what does not, and how the image models react to elaborate prompts compared with simple ones. In the end the prompt gave very reproducible results. It tells the model to keep the perspective, the tile pattern and the ridge lines exactly as they are, to remove moss and damage, and to change only the colour and the finish.

That works because the model can keep the structure of the existing tiles and only change their colour or surface. Putting a different type of tile on a roof is a different matter. Tile models often differ only slightly, and there is probably not nearly enough training data for them yet. Scale is missing too. There are large tiles and small ones, and besides the shape, flat or curved, the size decides whether the picture looks real. Image models alone cannot do that reliably yet.

How it works

The roof itself is edited by nano-banana through fal.ai. In voice mode, built on VAPI, the rep can ask for a colour while showing the tablet to the homeowners; OpenAI Vision gives the voice assistant a description of the building. For sales teams there are organisations, invitations, usage credits and billing through Autumn, plus QR flyers and a landing page for each sales rep, for door-to-door visits. Claude Code wrote the code.

Where it stands

Wertblick began as a pitch, became my entry for the Modern Stack hackathon, and I kept refining it afterwards when it came to actually taking it to market. The company I built it for did not go ahead with it, and I have parked the project since the end of 2025. The app is still online. If I offered it to a roofing company today, the offer would be simple: try it free for 30 days.