Your inspector should include going up on and looking at the roof as part of the house inspection - ask about this when hiring one, and if he says "I don't inspect roofs" ... don't hire him.
An inspector will also evaluate the plumbing and electrical systems, and you and your agent, or attorney handling the sale will insist that the seller bring them up to code, per the inspector's findings, as part of the condition of sale. The inspector will also look for signs of termite damage, with the seller being responsible for any remedial repairs, as well as termite protection application.
Go with the advice of the inspector, regarding the roof - asking a roofer to inspect your roof is like going to a doctor with a sniffle - you'll get a script for medicine - and will almost guarantee that he will want to do some kind of roofing repairs, touch-up, hot asphalt recoat, or even a complete build-up ... that's what roofers do ... roofing. If the inspector finds that the roof needs work, that too, will be incumbent on the seller, as a condition of sale.
Although the house looks very nice, It's hard to tell from the pictures whether the roof is 'even with the top of the shingle line or is it recessed' - it may include both, depending on the design, but most certainly will have a 'lip' of at least 3 inches at it's lowest point. Mine tapers with the appropriate pitch for drainage, from 2 feet at the front of the house, down to a few inches at the rear.
Built-up asphalt coated flat roofs should be recoated with cold fibre reinforced asphalt roof coating every three years to assure maximum protection against leaks developing - this is a job you can do yourself, although, over the years, I've seen the price of roof coatings increase substantially. I just bought 3, five gallon cans to do mine, and it cost
50 dollars a can - still cheap, if you can apply it yourself with a roofing applicator brush.
Flat roofs are constructed to conform to local building codes - a flat roof in Georgia may be supported with 2 x 4 trusses ... mine, located in Southeast Pennsylvania, is made from 2 x 10's, to support any snow load that can be expected in my area of the U.S.
Joe