GRP High-tops for Sprinter DIY?

[SpeaktoRobster]

Hi,
does anyone know where I might be able to buy a GRP high-top for a 2004 sprinter? I fancy creating my own DIY high-top with the Westfalia as my primary inspiration. I've searched everywhere I can think of (online) but to no avail. Quite a few places fo them for VW T4 and T5, and Reimo do a pop-up for the Vito.
Planning to buy a low-roof MWB sprinter (UK) if I could find the right GRP roof to install, failing that I guess I'll just get a high-roof MWB sprinter and make do with the headroom it provides.
Any pointers would be appreciated....
R