@Jeff Dinehart so you have done some inspection and it sounds like you know what you are looking at........you still need to look at the roof and foundation and walk every unit.

Plumbing leaks may void warranty.

The duplex has a slate roof that is need of work and some exterior paint work needed and basic turnover of the units interior.

However, as a result of the aforementioned, the demand for contractors has gone through the roof.

On the other hand, an inspector that has a narrower focus (i.e. roof inspector, termite inspector, structural engineer, etc.) might provide better insights on specific potential issues.  

My question is when looking to rehab a house to put on the market for rent how do you know how much longer the bigger ticket items will last such as the HVAC, Roof etc?

. $40k is the price she offered to sell it to me for and it's already in livable condition alongside a new roof, new windows, new furnace, and remodeled bathroom.

I am 22 now, I dropped out of college simply because I don’t believe in the student loans and knew I could do big things without it and always had an eye on real estate.I started up my own contracting LLC as I have a construction background of about 5 years from concrete to roofing and everything in-between.

I also would caution that $1000 a year for maintenance may be low when roofs up here get 20 years of service so really you should budget $600/yr for the roof alone not to mention water heaters, furnace, A/C units, appliances, flooring, paint, updating kitchens etc.

You could make an offer with a due diligence period to give you a chance to get inspections, and check for any environmental issues (cars leaking fuel, oil, etc... could be an issue).