I had a 2000 Coleman Westlake bought new, kept it for ~2 years, and had no issues whatsoever, if that helps!
It's very easy to see if you have a bad roof because it will look like it doesn't have a nice, tight uniform seal around the whole base of the camper when it's closed. (So, in other words, it will look "off" or warped, and the clamps that hold the roof to the base of the unit will be very hard to close because of the warping.).
Not all had this issue, but enough did that it made the rounds online with people (rightfully so) complaining about it. As second owners, a lot of people had to replace on their own dime since the original warranty wasn't transferable, if I remember correctly too...
Keep in mind too that there were a lot of these Colemans sold in the early to mid 2000s and many people didn't have an issue (and lots of happy folks also don't post online!).
If everything checks out (good canvas, lift system is good, underneath good/no rust, no water damage inside, wheels/bearings/axle in good shape, etc.) and the unit has been maintained well, then I would say go for it!
For added peace of mind, maybe consider having a 3rd party inspection done too, if that would help you. A local dealer or possibly a Camping World should be able to accommodate this for you. A basic safety and general condition check.
Keep in mind that this unit is still 10 years old, and things can and do happen, even when well cared for. It's just the nature of the beast. Best any of us can do is check everything to the best of our ability, and then you just have to take that plunge on a rig that's right for you!
Best of luck!