Would this drain all of your funds? 

Flat roofs do drain, but not nearly as efficiently as a roof with any kind of pitch.

As soon as I and renewed the lease the tenant wrote me this long message with all these things wronge, including drain smells bad(she’s been putting bleach down the drain to kill the odor, the lights in the kitchen and bedroom are flickering(this ones easily fixable) & the bathroom floor is in-caving because of water damage(she suggested a new shower door).

My friend also happen to have a drain line in running through the backyard so "winning ".

For instance the one I am buying has stucco exterior, new roof, dry basement, new furnaces (3 of 4), new hot water heaters, new plumbing (except for some of the drains). 3) Vacancy - My four unit has only had one vacancy in 15+ years.

I found out that it was because they had problems with the water draining wrong.

The owner called and wanted a replacement as well as fix the outside siding where the pop-off drained off to.

This might seem very unconventional, and this is totally just my own opinion, but maybe you should just take a look at what the most is you are going to get out it financially after lawyers, and decide if this is really worth the emotional drain and continued hurt.

Rehabbing houses is a endless cash drain.

You need to use a live answering service or else you are throwing a lot of money down the drain, because those sellers will quickly call someone else.