What's fair in this partnership?

[Elena Nelson]

My brother is moving to an expensive area that he can't afford right now. He would be able to have cheaper monthly payments buying a place versus renting. 

He wants to go in on a condo together. That he would be living in and paying utilities. 

My question is what would make this partnership fair? We talked about paying 10% each for the down payment and 50/50 for any repairs. What would be fair for monthly payments, taxes, insurance? 

I'm not trying to make any money until we sell it so I am not expecting rent from him. Basically I don't want to do anything unfair towards him but it's also a way for both of us to make money selling the place in a year or two. Any suggestions?