Whether I got a deal or not on a roof is irrelevant, you should be concerned that the roof is 4 years old.Additionally, I do out RET on mine, but you can typically hop on a county assessor site, plug in your purchase price to see what those will be for YOU. 

I would love to be your "boots on the ground" type person.

How do I structure a fair and decent term/s for items like roof and HVAC?

Here's a link to my estimated calculator report if you guys are interested: Portland Duplex Austin- I was able to shave off $4000 based on the inspection that suggested I needed a new roof within a few years.

The owner told me she just replaced the floor, roof and heater/ac.

Complete remodel from roof to basement and everything in between - new kitchen and bathrooms, flooring, light fixtures, paint.

Do you know the condition of the roof, water heaters, etc?

Construction (stucco siding and tile roofs, I have several 20 year old roofs that should go another 20 years in their sleep, I paid $7500 to reroof a 12 year old property on MN) and age property.

A couple of thoughts:The best quote I recently received for a roof (1,700 square foot ranch - SF BayArea) was about double that of your budget item;  the electrical line item also seems low based on charges I am seeing up here ($100/hr -$120/hr) and what I understand will need to be done (essentially wiring an entire house)

New roof, upgraded electrical, plumbing, etc.