My question is, how do I get funding for a project like this? 

If you are self GC for the project you will also need Liability for that exposure. 

If the total cost of your project is $400k, then the down payment on a construction loan should be 25% = $100k.

If you buy a 4-Plex and decided  to pull a permit for one Unit to start your renovation project and not the other 3 can the building inspector (plumbing, electric) mandate that you show the other 3 units during the first unit inspection ? 

Just about to finish up a 7 month rehab project.  

That will help you understand if it is worth it and what your actual return on this project is.

It does no good to place capital with someone who has a great project with an attractive pro forma, to find out later they can't be trusted. 

There are things that they would be entitled to in terms of a price adjustment (in your example, if lumber prices skyrocketed for a specific reason beyond his control then usually the owner is on the hook, however, there are measures to limit this exposure).A contract can be drafted using the scope of work, estimate, and schedule (you can include liquidated damages - this is a sum (not a penalty) of what it would cost you if the project is not completed on time - think daily rent and storage rates). 

For my current price range, it will most likely be a small project house.I would like to network with a general contractor to get rough repair costs before going into a property with the intent of hiring them to execute the work.

I would like to know what is the equation, or metric that I should use to judge one potential project vs another in terms of cost and the potential increase in revenue that money should create.