That is so weird.Regarding nailing down repair costs, a lot of GCs will do a pre-purchase walk through, and give you a decent estimate for around 100.00, sometimes less.One thing that is good practice is to first make an itemized list of everything you can see that needs work, and take a stab at estimating it.

You can get a pretty good idea of the magnitude of your overhead costs with just a little homework to nail down your expected costs for some of the big ticket items like property managment, property taxes, hazard insurance, and association fees, For a single dwelling unit, use one month rent as your vacancy allowance if you are in a strong rental market.

In my area, depending on the town, polished STR's have 75% - 85% occupancy.

Nail on the head, Steve Babiak.

A few folks hit the nail on the head. 

@Jose Martinez Kent Ritters post really nails what you need to look for in a market.

@David Benton-  if you havent already tried  locating and contacting the owner of the property - try this  tactic  .... if you have a local realtor  that you work with - maybe ask them to intiate contact as well  ....if you need  assistance determining of what is possible for the dadu/ adu   on the specific  property - you might have a  real estate type attorney  review and assist  ...finally  - make sure you have  financing  lined up  so that  you know this is possible once you nail down anf  find a  property

You were the only commenter, and seemed to have nailed the response!

Additionally all roofs require a permit even if you are only doing shingles, because the state requires updated nailing even on shingle replacements.

My investor friend & son who pay their CPA >$1600/yr for tax advice & tax prep got nailed for $70k in taxes after selling several properties.He was commiserating that his CPA neglected to advise them on a basic rearrangement of tax deductible repairs etc to offset the taxes he paid.