There's a lot of material here on Biggerpockets to help you get a a better idea of how to research rents, and property values, learn about what your actual expenses of holding a rental would be, pros and cons of various areas, etc.

In a month or two, you'll be a regular ol' material expert at REI and ready to take action.

It's going to much be more expensive to replace 35 square than 20.How about the plumbing and drains - what materials are they?

I could throw a rock and hit a house 4 houses down with 1 extra bathroom that appraised for 68k and its the same materials...  

The big thing is that you have to disclose what you are doing upfront and then do not deviate from that plan (a material change) without going back and getting the investor's permission/sign off for making that change to the business model under which they initially invested.

Just ordered Brandon's book . lots of material to absorb. 

If something goes wrong in the build, and if you structured all the llc correctly, you could simply declare foreclosure/bankruptcy on the llc, don't pay material, contractor, or labor without them holding anything.

Simple math:   (Average hourly rate) * (crew) * (days) * (8 hours) = Labor costThen get the material cost. 

Read through all the free materials in the forums here.  

But you'll find the best WHY from personal development or business philosophy from material from Jim Rohn or others.Cheers!