Do they want the exactly shape of a surfboard in terms of the rails, for example? If they want to use it as a shelf I would almost suspect that planing the rails on one side would be best and making the rear flat so there is more of an edge against the wall. If they want you to basically build a 5' surfboard then you'll cut and shape as normal.
I've taken part in one surfboard build for riding not for shelving. There were templates and such that were made to get things right. I was under a lot of supervision by a board maker.
He doesn't want a long board, he wants a 5' board with 3 fins under it. I worked up all the costs and I build in buying a cheap used board with shipping to use to make templates. =) I hope he goes for it.
As for the top I'm going to confirm with him today but I'm assuming its going to be flat and just the lower part will be profiled like a surfboard. The shelf will be floating so none of the board will actually contact the wall.
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