FYI, not all roofs have plywood in them. Newer motorhomes have walls and ceilings made of a composite plastic material that is heated and various materials are sandwiched together and compressed. Newer motorhomes, even Class Cs, also have aluminum wall "studs" instead of wood. Aluminum and plastic is better than wood because wood rots and loses strength. Whatever you buy, make sure you know what is in the walls and on the roof.
Also, even with 66,000 miles, I had my brakes checked last week and was told front and back were at 70%, which really pleased me since I am a lifelong left-foot braker, and whose sons are constantly complaining that I must be riding the brakes!! Ha! I did have a problem last month with wheel bearings, and ended up getting them adjusted, but driving too long with the problem and messing up one tire. (Was in Canadian Maritimes and could not get anyone to work on it.) Cost to get them adjusted and greased was $200, which was not bad considering they also rotated tires and checked tire pressure in all.
And those seven tires would have gone for about $300 apiece. I had bought one and got reimbursed for it after a sideway blowout, but I probably could have gotten a better price if I was buying a whole set and if I could have shopped around more. The problem is that repairs or replacement of things do not always happen in places where there are a lot of places to shop around!
I do think you ought to buy when you can camp for a couple of times and see what does not work. But I also agree that you need to buy based on floor plan and what fits you. Mine is perfect for me, and I got it right first try, buying new, but I did a LOT of research!