What is my percentage in building new multifamily with a partner

[Eric Teran]

BP,

I'm an Architect. I'm good at that. I get permits fast and have nice designs. One of my clients is a developer and is good at finding properties and running the numbers (not good at that). I like that he is conservative and patient. He found a lot and we have decided to team up to build a multifamily building containing 18-22 apartments. We are still working with zoning but the initial numbers were based on 15 apartments. So already we are ahead of our initial concept that provided cash flow. The idea is to hold onto the property for at least 10 years collecting rental income. After that, we would be open to selling. 

How do I figure my worth as a percentage in this partnership and make sure I get a fair deal during the next 10 years and when we eventually sell? Whatever we agree too I will have a lawyer look at it before I sign anything. Any recommendations for a lawyer in the DC area?

My normal fee for this type of project would be around $80k which I would collect throughout the design and construction process which would last 18-24 months. My investment is my time and obviously charging no fee. I would also be doing about another $30k of additional work to coordinate everything during construction as I would be acting as a construction manager. 

My partner is also investing his time, some money and we might have to find an outside investor. Once we have more detailed construction budget (2-4 weeks) that will be determined. 

Hopefully that was enough information to get some feedback. Thanks BP!