Rails Developer

The client is a developer who is working on a learning platform for companies.
He will be in Berlin from mid/end September on and is looking for a Rails developer to work with him on the platform for 2-3 months. Afterwards he will test the system with a few companies who already signed up as beta testers, and if the results are positive, the project will be developed further.
The first 2-3 months the client would like to sit in a coworking space together with the developer (which one is not yet decided and can be agreed on with the freelancer).