But, given that he has a primary residence there already that he must leave (Army doesn't give much choice on location), if he isn't able to sell the property quickly for at least break even, and can't take a deduction for a loss, my thinking is to flip it to a rental (question is which kind makes the most sense), he should be able to cash flow given his monthly expenses, even if only $100/mo, then if he still sells for a loss in a year or two, he could take a deduction.  

Please let me know what you think.thank you for taking the time to read through this. 

Never built in Houston before so take my feedback with a grain of salt but I'd put money on it being impossible to build a duplex from scratch for $125 a foot (including everything from drawings, engineering, permit fees, general conditions, labor, material, landscaping).Out here in AZ the builder cost is going to be $200 a foot at best, but add 20% on top of that for the client cost.

You could get into that field but it takes a lot more resources and legal knowledge and support. 

You can take advantage of the free resources here like the BP podcasts and forums.

EDUCATE YOURSELF - yes, it will take time, but will lead to a selection that better meets your expectations & avoids potentially costly surprises!

The property owner contributing the land as equity takes it from a good deal if everything goes right to a real no-brainer. 

Quote from @Michael Nelson: Hi everyone, heres my BRRRR situationpurchase price 520,000rehab 25,000Appraised at 600,000Rents are now at 1950, 1850 and 1600 totaling 5400My question is can i get a DSCR to take out all 545,000 as the rent roll to to a mortgage for that amount would ratio out to around 1.4 but....obviously appraisal is not high enough for 80/20Any info on this or suggestions would be great.

Would it be possible to take my $100,000 liquid cash and their equity and go to a lender and get some sort of funding for the rehab?

As @Daniel Hyman said, getting into the 3+ property range can overwhelm people and take too much time.