I did not see a 196RB, in Jayco's line up. I suspect you have a 195RB?? Edit: I see you had both model numbers in your post. So I bet it is the 195RB!
It has a 810 pound CCC, which includes propane, batteries, water, and all your stuff. If you purchased a Thule roof top box (35 lbs), plus a bunch of aluminum standoffs, mounted to the trusses. Your added weight with a ladder will be around 100 pounds. Now add your stuff, and you'll have another 100 pounds. The TT roof can hold 200+ pound person, so the roof is an option, just secure it to the trusses, and make sure to do a good job sealing the penetration points. Inspect the roof every 6 months or more frequently.
Personally, I think I would consider a few other options first;
What items were you thinking of putting up on the roof?
What do you have for a TV?
Couple options, have a weld receiver hitch added to the back of the TT, and use an Aluminum cargo tray. Need to be careful with this option, as you can lower your tongue weight which can cause sway issues. You still have an 810 pound CCC, you eliminate the ladder, and a lot of required framing, and potential water leak points. I suspect your overall weight will be lighter than the roof option.
Could you put a roof rack on top of your TV? lower height, easier to access, could install two Thule like roof boxes. Possibly no ladder required.
Jayco 195RB specs
28 pound AL cargo carrier - could be used with the TT or the TV when needed, and not always used.
Thule roof box 34 lbs
Let us know what you decide to do. Especially if you go roof mounted, like to see how you mount it.