To do it "cleanly," you'll have to use commercial lending instead of conforming residential loans which legal entities are eligible. 

I wouldn't rent a non conforming bedroom.

The sellers are acting in good faith here, there plan was to nt have lots larger than 1000 sqft built bc it would take away the natural light they get on their large home next-door , they agreed to try 1200 but that was not conforming to code.  

Has 1 conforming and 1 non-conforming Bedroom in the basement7.

That is different from conventional conforming fannie/freddie type loans.

Has 1 conforming and 1 non-conforming Bedroom in the basement7.

Will you have a conformed/signed contract?

Because I live there, I got a standard conventional conforming loan. 

The vision must conform with zoning, meet a need in the market place, be built within the market pricing so it can be financed.  

Any lender using conforming loans will have to meet those guidelines.There are plenty of lenders that do allow LLCs to hold title.Some of the advice here has been incorrect, or not clarified.