My previous coach was a 2009 Phaeton. The roof was installed as LtDan described. I had the coach for over 8 years, and while I had other issues that I'll outline below, I never experienced any 'play' in the roof.
The fact that the roof shows signs of fresh caulking may or may not be a good thing. If the caulking was applied after roof leaks were discovered around vents, etc., the the damage has possibly already been done.
One possible way to check is to take measurements while you're on the roof of where the soft spots are. Then go inside the coach and try to find the same locations. Remove the roof air conditioner outlet cover and/or the return cover, as close as possible to those locations, and push up on the ceiling foil inside the duct work. There should not be any 'give'. These areas would most likely be close to the fresh air vents.
Now there are some known issues with Tiffin coaches of that era.
1. Roof rail radius cracks - The roof is one piece with radius edges that make a 90° angle to line up with the side walls. The roof radius portion can devloped hairline cracks due to thermal fatique. The cracks will start off appearing as fine white lines, and will eventually get worse as they open up more.
2. Wet bay floor rotting out. The wet bay floor is wood and is subject to water intrusion, thereby rotting out the floor. The way to tell is to crawl under the coach past the wet bay fiberglass pan, and poke a screw driver into the floor panel. If it is soft then it is rotted.
3. Front DS slide floor rotting out. There was a problem with the floors rotting out due to water intrusion. The entry point is at the bottom corner of the leading edge of the DS slide. Water enters through that opening and eventually can weep through the whole slide floor. This one is a little harder to detect, but if you see an opening at that bottom corner of the slide, stick a sharp object in the opening and if the wood feels soft then it is probably rotted.
These items were so prevelent on coaches from 2007 to 2012 that Tiffin had dedicated service bays in Red Bay that only handled these repairs. They were covering 100% of the cost, but I don't think that is the case any longer. I had all three of them done to my 2009 coach at no cost to me, but that was quite a while ago.
If you're buying from a private party I would suggest asking if any or all of these items were repaired, and have them provide proof.
If you're buying from a dealer then they should be able to contact Tiffin with the SN and find out (I don't think Tiffin will provide this info to a private party just interested in purchasing a coach).
On edit: I just happened to see you're located in Spokane Valley (we used to live in CDA). Tiffin has authorized service centers on the west coast that can handle these repairs, so it doesn't necessarily mean a trip to Red Bay.
Bob, Sherron & Kinsey (Goldendoodle)
2017 Tiffin Phaeton 40QBH
2014 Jeep Cherokee Limited