The variance in percentage has to do with a combination of several factors.  

Craig, More Factors here than what you have listed, but for a QUICK Evaluation in Self-Storage: 1.  

Also, if it is not too expensive, one entity can be exposed to lawsuit but another entity to hold the asset.

Location is probably the most important factor of it all.  

The combination of BP information overload, books, Brian Gibson, and deals that don't fit into the wholesale category exposed me to the "terms" side of investing.It's listed on MLS with an agent. 

With all of these factors coming into play.

Many other factors can influence the ultimate returns these projects generate.  

@Kodie Altvater costs are ultimately a factor of 2 items, if you're efficient: labor+ materials.the goal is to arrive as close as possible to just those 2 factors with as little add-on as possible. add-on being profit, a companies overhead, etc. labor and materials are unavoidable (as well as other stuff like permits)....so how does one arrive at those costs?

Make sure you factor that into your numbers. 

Amenities are fine to consider but the major factors are going to be bedrooms, baths, square footage, location, and quality of the unit.