If you keep rolling one 1031 exchange into another until your time on Earth is up, you will not only have deferred taxes on your gains each time, but you will have accomplished the seemingly impossible: avoiding taxes altogether.

Buy supplies in bulk and keep them in a locked closet, garage, ect.

When I hear "affordable" I always think, undesirable since price is always based on supply and demand.

I do not understand why one looking for a buy would ever go to a "wholesaler" vs those who actually control the vast majority of supply. 

My friend is going to supply the money for the down payment.

There are suppliers in China who can supply pre-cut SIPs and they say they can source other exterior and interior finishes (except electricals and plumbing) from other suppliers and ship it.

I was concerned because the tenant has roofing supplies all over the back yard in addition to a trailer and roofing machine in the street. 

You can ask the Sub's, or whoever you are going to do the work, which materials they need and price them out at other supply houses.

Plus the resources Africa supplies.  

I have done wholesaling in the past (not in RE, but in reverse supply chain liquidation), and had to deal with a lot of unethical and dishonest sellers.