new member, my first post so be nice!

I've been looking for a roof bed for my 89' westfalia california high top for a while now but to no avail
The previous owners of our van had the roof bed removed. the side runner rails are there but no upper bed.
Just wondering if anyone has pictures of one in situ and how the mechanism works. Im wondering if it would be a difficult job to make one up.
A few pictures of the components would be really handy so I could get an idea of what is involved.
cheers
barry
P.S. even better if anyone has a spare westy upper bed left over from a hightop to poptop conversion that they want to sell!