upvc covering Wood conservatory

hi
I have an old conservatory that has a woodern upper part that meets the felt flat roof.
This woodern part sits above the glass windows and I am thinking of putting a upvc covering onto this woodern upper part.
Just wanted to know if I fit the upvc direct onto the wood (no air gap) is there going to be a condinsation problem as upvc would be touching the wood.
Should I try to make a stand off gap so air can curculate between the wood and the upvc sheet ?
This old conservatory was built in a odd shape and is difficult to keep waterproffed hence the reason for the upvc covering.

If the wood is sound the upvc would be adhered tight to it.

Hi Alstairreid
Sorry slow in reply, thanks for the info, will do as you surggest, its my next job of many.