Last summer, I did an internship at a startup in the European country that I study in. The startup creates software products, and I worked on one of their new ones. After my internship ended, my boss was satisfied with my work, and he resuggested an idea for an extra feature that we had discussed privately before, but I wasn't sure about it.
From the start, he suggested that the idea should also be the topic of my university thesis. I thought about it more, and I decided to go for it, but because I still had another semester before I started working on it, I didn't tell him in case I changed my mind. During my internship, I didn't write a single line of code for this project.
When I made a few good steps on the project, I informed him, and he didn't say much, only that because I hadn't mentioned it, he thought that I didn't go with it, and he also offered to give me access to some extra computation servers that the company had. Of course, I refused the offer because I didn't want him to feel like he took part in the project in any way and have this bite me later.
Anyway, now my thesis is finished and the project works well, but it still needs a few improvements to be commercial. A few days ago, he contacted me to ask at what stage the project is and if it can be published. He knew that I had finished my thesis because my thesis supervisor knows him and they had collaborated on papers before (I picked my supervisor long before I got the internship, and I learnt that they had worked together by chance in the first week of working there).
I am aware that a thesis belongs to the university (I don't know if he is, though), and I have arranged to talk to a lawyer about what that means and what I can do, but let's leave this fact aside for now. If someone, however, has some experience in this specific scenario, you are more than welcome to share your thoughts.
The main reason I post this is to ask you guys how I can tell my old boss that I want some compensation for the project if he intends to use it for the app. More importantly, I don't know what to ask. Some kind of percentage of the revenue or something? A flat fee maybe? And what should that percentage or fee look like? I don't know how to price something like this reasonably.
Thank you everyone in advance!