My budget for purchasing homes is $20,000 each including the moving expense if possible, this is the top price I will pay and only vinyl siding and shingle roof will do, also it must come with central heat & a/c and appliances.

Ventilation is key...not only in naturally cooling you home but, without it, your shingles will age prematurely.  

Re shingled the roof, and some plumbing work.

The biggies (read, "expensive to fix") are:1) Severely Clouded Title *2) City/County/IRS tax liens and/or special assessments*3) Mechanics' liens *4) Soil contamination5) Bio-hazard6) Roof (watch out for multiple layers and shake shingles!)

If the mobile home does not move or shift then it is essentially a box that can be built to any standards.Many of mine have 2 x 6 walls, insulated thermal windows, metal or shingled roofs, three-quarter plywood floors and many other features that house’s do.

We have a particular type of shingle (T-lock) that most insurance companies will not cover but that's because of the high failure rate, not because of age.I also don't understand why they wouldn't cover an out-of-state investor.

And our systems are all computerized.

(I'm house hacking and don't plan on staying there for more than 2 years, so I wouldn't get too comfortable with my garage space), plus the extra income is more appealing to me anyway :)  So my questions are:-will fixing the garage structure and getting the roof done (re-shingled) have a decent positive affect on the property value? 

Three units have no coverage for roofs as they had T lock shingles when I bought them and have not replaced them. 

Also-vinyl/shingle with three bed rooms are the best.