For example we replaced a water heater recently.

Based on rough assessment, the following is needed just to get it listed:NeedsLowMidHighRoof$7,747.00$12,580.00$26,037.00Siding$20,000.00$25,000.00$30,000.00Windows$9,000.00$12,000.00$18,000.00New Deck$8,000.00$10,000.00$12,000.00Roof Leak Repair$2,000.00$3,500.00$5,000.00Mold Mitigation$1,000.00$2,500.00$3,500.00AC Units$13,000.00$15,000.00$18,000.00Carpet Replacement$2,500.00$3,500.00$5,000.00Kitchen Remodel$5,000.00$10,000.00$20,000.00Total$68,247.00$94,080.00$137,537.00Due to lack of capital to fund these repairs, I believe the best option is to find an investor looking to flip. 

Let's say you were replacing windows.  

For example:-A tenant complained about the AC not cooling, so I replaced the entire unit with brand-new equipment.

Disallowed losses under wash sale rules increase the cost basis of replacement securities, potentially reducing future taxable gains.This post does not create a CPA-Client relationship.

If the roof itself is not covered, you can estimate your out of pocket if the whole roof has to be replaced. 

Yes, that makes perfect sense, especially in such a large transaction to find the replacement property.

Do you save three months of vacancy for each unit and $50,000 for the roof replacement?

February may not be the best time to find a replacement tenant, so you may want to go Month-to-Month (MTM) until April or so.

This is a fundamental component of the BRRRR strategy that I have yet to understand.Or, does it not make sense for the friend to invest in this deal if they're primarily looking to flip?