Just missed out on an old windsurfer at the tip shop few weeks back - not quick enough - would be ideal for a longboard .
Few different techniques you could use - some use a vacuum bag ( I don't have one ) and timber veneers .
I use a thicknesser to bring the timber down to about 6 mm , then a table saw to cut into 4.5 cm and 2.5 cm strips . Use the wider strips on the bottom side and rails , thin strips on top deck - as you get closer to the rails the timber needs to bend front to back ( rocker ) and side to side due to the curve on the deck . I soak the timber strips in a water tub for at least put 24 hours with a weight on them to get the bend for the rocker .Then using narrow strips allows you to mould into the curve of the deck .
there is a YouTube video - how to make a wood wrap over foam surfboard by deep creek TV . Probably explains it better then me .
Square rails with sander

Glue and clamp / plastic wrap strips on deck and bottom
Cut shape with circular saw
Rough sand deck and bottom - aim is to remove lumps / high spots then glue on rails ( putting 4 layers on this one )
Then add nose and tail blocks ,fine sand top / bottom , shape rails and nose / tail