I recently graduated from Architecture School and have 6 years of experience with construction project management and construction cost estimating.

Break ground May 20 and it estimated to be a 8 month build.

How does that compare with your estimated loan payment, property taxes, insurance, utilities, etc. 

I also posted on DIY forum and that helped give insight on what to do about my shed but no help in finding folks to make the changes or estimate cost.So basically looking for 2 separate contractor needs, would like referrals if you have any.

I've started to try and analyze properties, to get into the practice, however there are several variables that I do not know when it comes to estimating. 

An estimated 185,000 households are behind $6000 in rent. 

Rental estimate is under $1000 per month and you have $2800 as monthly rent.

The experienced plumber that he recommended to us originally gave an estimate of roughly $5k to change the pipes, but with permits is charging $11k.

Would I need to get an contractor estimate before offering this to cash buyers?

It is YOUR estimate of what a property will be worth after you have completed whatever kind of rehab work you intend to do to it.