You might expect a shingled roof to last ~25 years because the shingle might be rated/warrantied for that period of time, BUT if you monitor and do repairs as they come up it can very well last 30, 35, or even 40 years which to many people sounds crazy but since roofs are expensive those extra years are like gold!

I don't touch shutoff valves etc. unless they look to have problems.Roofing is always 20 year shingles.

On page 29 it says that Sheathing ranges from $30-45 per sheet then below that it says Roof Replacement for asphalt shingles is $150-400 per square.

Example for my market: - water heater $1600 (lower end of licensed plumber cost), 12.5 years (150 months) $10.67/month- roof (asphalt shingle) 2 br, 2ba typical size ~$10k licensed, 20 year life span $41.67/monthkitchen, exterior paint, flooring, plumbing, electrical, fencing, tree trimming (I have a property where the tree trimming is one of the larger maintenance/cap ex items at over $1k/year), bathrooms.  

I had a wind storm rip some shingles off one of my rentals a few months back, still fighting them and trying to get ahold of the "right person"Stick to it, don't let them not pay.

Panels can be lifted up by hand, the ridge caps aren't actually ridge caps but someone bent metal pieces to DIY a ridge cap, the roof isn't vented, and no underlayment between the asphalt shingles and metal roof. 

Wear such as granule loss, exposed fiberglass, biogrowth, nail pops, and/or buckling shingles was observed.

If shingles are broken or missing, leaking, rotting, etc, that's a defect.

The roof was so old that most asphalt shingles were down to just the base fiberglass base material.  

I had 2 - 30 yard dumpsters brought in to hall out the plaster and the old roof (which was like 8 layers of shingles).