The interesting thing is appraisers don't often realize or give huge credit a new plumbing, new electrical, new HVAC despite these items being very expensive.

Ultimately, it comes down to underwriting and the ability for the property, and you, to afford to pay the monthly expense of the loan. 

Hello Dana, For that purchase price in Brooklyn, NY, you could be looking at considerable unknown expenses at this point.If the property is occupied, you'll have to factor in attorney fees and holding costs while you wait to gain access to the property.Furthermore, you could be facing additional costs related to title issues: open permits, violations, liens, judgements, etc.

The purchase cost is on average $350k - $450k.

My thought is to help him out by going in 50-50 partnership for many reasons: half down payment, half capex expense, strong co-signer on loan, me being local to investment property to take care of little things that need attentions (he will be out of state for his job/I will have PM), etc.  1. 

My opinion doesn't change, this could be a very expensive ommission.  

All options seem pretty expensive. 

Additionally, it provides investors with the opportunity to add a unit on a property they already own, simplifying management since the new unit is in the same location.Finding a vacant lot is both expensive and difficult, so the ability to build, subdivide, and create new development opportunities can make financing easier.

Unless the borrower is self employed and takes a lot of expenses to show lower income on their returns then it usually makes sense to pay a couple thousand a year in higher interest (you can pay like 4,000 a year in additional interest for DSCR if you are saving 30+k on your tax bill kind of math lol)

I'm kind of a purist, but I'm hesitant to put in an all new floor (pull up the old ones, level the new wood flooring on the beams) because A) It's expensive B) it's a loud, big job and I have tenants on the floor below.