If you rule out rubber (synthetic fabric) roofs, you rule out at least 90% of what is made today. Fiberglass sheeting is used on only a few brands of motorhomes (but including some of the best selling) and metal or molded plastic shells on only the most expensive RVs of a given type and size.
The advice about "entry levels" is also bad, because among manufacturers that have "entry level" and more upscale product lines, the value models (a better name) have the same construction quality as upscale lines, they just aren't as ostentatiously fitted out. Go upscale there, you are buying more glitz.
If you are on a budget, particularly if buying new, entry (or value) model lines from major manufacturers are the most RV for your money. If you want to spend money, you don't go upscale with them, you go to a manufacturer that puts the money into building a better RV. Also, one manufacturer's entry level model (e.g. the line with the lowest prices) might be priced like someone else's line two or three levels up, but built better than anything they build at any price.
On a budget, you should be looking at volume manufacturers like Forest River, Coachmen, Thor's Dutchmen and Fourwinds lines in towables, some of the cheaper lines in Thor's Keystone brands, K-Z, Jayco, and a few others like Crossroads.
In motorized, again Forest River, Jayco, Thor (formerly branded FourWinds/Chateau/Dutchmen and Damon) and Fleetwood. But don't pass up higher quality possibilities like Winnebago, Monaco/Safari/Holiday Rambler, Newmar and Tiffen if shopping motorhomes and shopping used.