x2 on checking the tires, as well as other high-dollar items like roof A/C and generator function.
My '94 had similar mileage when we bought it, but the tranny was recently rebuilt. Make sure you have enough extra money socked away for that potential expense, should it be needed. As Gary said, rigs of this vintage are operated at the upper capacity limits of the engine, tranny, tires, etc. so you don't want to take chances there.
What do you mean the "roof might go two years or so"... ? RV roofs don't just automatically fail at some interval. You can re-coat it every few seasons as needed, or seal the seams with Eternabond tape and many of us (myself included) have done. Roof maintenance is definitely something to stay on top of, to prevent leaks into the ceiling/walls of the RV. Don't wait until you KNOW there's a substantial leak, because chances are there has been a small one for quite some time before noticing.
Check the Library link above, and find the Buyer's Checklist for used RV's. That will give you a whole lot of things to check out when you inspect it.