Yikes, that is heart breaking. How much snow did you get? I seem to recall reading on TM's website that the roof is built to sustain 2 feet of snow. They don't say anything about ice, though.
Obviously the original design and construction is the best way to go. Anything else will be sub-optimal, but it may indeed be cheaper. But I'd at least consider original construction first. One suggestion is to spend $200-$300 and fly down to the factory to take a tour. That way you can see exactly how it is constructed, and perhaps closely mimic at least the design and materials, although you may not be able to use the same construction technique (like adhering the aluminum to the foam).
Another idea is to buy this salvaged 3124 on ebay:
http://cgi.ebay.com/ebaymotors/ws/eB...m=110411905761
...and salvage the roof, and part out the rest. I wouldn't be surprised if you got $1000 for the appliances alone. The guy says he also has a 3023, which might be easier to fit. Or wait for a salvaged 3023 to appear.
Dave