Development fees for small residential project

[Ven Bodavula]

Hello everyone 

Need advice on what is a reasonable compensation to provide to a developer helping  me 

Project is 2.5 acres of residential land - was developed for commercial office buildings , recently rezoned to residential with all utilities laid out . 
I have the land under contract , working with a developer who develops , residential lots . 

He is kind of slowing down and father of one of my colleagues and willing to help and get involved with 30-35 years of experience doing this . 

Land with development cost will be be around 800-900k, which I and my partners will contribute  and projected  expected  return is around 50% . 

What percentage of profits is reasonable fee for him to be the developer , doing everything from permitting to lots ready to build