How to charge a percentage of the rehabber's net?

[Sean Dezoysa]

J Scott mentions in his book that an excellent way to get into rehabbing is to wholesale a deal to a rehabber, and give him the deal for nothing up front and 10-20% of the net + being allowed to shadow him throughout the process. Sounds great, but I only know how to assign a deal for a fixed fee.

How could an assignment contract be written to charge a percentage of net profit on a future resale? (Or is a more complex agreement needed?)

Thanks