Ask HN: Project based pricing or try and build a Saas app?

Don't know which way to go on this one, client needs a work order + inventory app. I was about to simply quote a price for a bespoke app, then thought why not charge them nothing... build the app ourselves and have them subscribe to it as the first customer. I would ask that they pre-pay a year on sign up.

One possible issue arises if they decide they don't need it after I've already paid to build it.

There has been a lot of discussion on project/value based pricing vs hourly, but how about we throw subscription based pricing in as a third option?

Thoughts or suggestions?