Fibreglass roof for Roll off roof observatory?

[michaelmorris]

I'm in the final planning stages for a new roll off roof observatory in my new house.  It's going to be a completely self-built structure with oak uprights and top rails for the roof support pergola.  As on my old observatory, the plan is to have a lightweight roof opening and closing by hand and simply running on rubber wheels on the horizontal rails with rubber wheels retained by a simple outer retaining batten on the outer portion of each horizontal rail.

I used this arrangement very successfully for the metal shed-based roll off roof observatory I had up until 4 years ago.  This time instead of a thin metal roof, I was thinking of using a custom-built lightweight curved fibreglass roof ( like a shepherds hut) with wooden strengthening.  These appear to be remarkably cheap to have made (around £400).

So here is my question - has anyone else used such a roof for a roll of roof observatory roof? 

What (if any), problems did you encounter?

Thanks