Have a read... It will give you an idea of how boards are made. But be warned that if you go down this path you may end up spending all your money and have a pig of a board.
boardlady.com/anatomy.htm
consult a board builder, show him your design, how you want to do it. If you feel confident about the shapes, do it on your own, but maybe try to copy a veryfied shape fro the first time.... I made a shape on my own, next month I start laminating sandwich (needed $$$ for the material)... I will pay a board builder for vacuuming and all the needed material for it (peel ply, bag etc.), he will also advise me how to do all the dirty work, since I'll do it at his workshop.
I am trembeling in fear to see whether the board is going to be functional or not. I made it short, wide and a nose rocker in a freewave spirit ... 225cmx65cm, bottom is more or less flat, with a bit of vee from 1/3 towards the nose. Hope it copes well in chop, I think it will do good on flat water, but also hoping for small waves up to 1.5m :)
Volume of the blank is 87L but I expoect additional 7-9L when adding all the material on EPS core.
P.S.: jermaldan gave you a very useful link to get a view into all the important parts of a board's shape and understand their meaning.
check this topic, a lot has been said.... www.seabreeze.com.au/forums/Windsurfing/Wave-sailing/bigger-wave-board-part-2fat-btard-wave-sailing/?page=1
Not to put you off as it is an aweome project but you need to have a looong chat with somebody who does custom sandwich boards. Or at least....
Have a look at www.ecboards.co.uk.Menu on the left side down the bottom is a how to section.
That will show you how involved it is - and it does not even cover the very complex area of designing a shape that works.
If you read every last bit of that and still wanna do it, go for it!
I had a year or even more of just collecting the data, now I've shaped the EPS, next month it's laminating time...
heres an old longreef express after removeing all the glass and reshapeing 
get in contact with RIDER
the best custom shaper in perth by a long shot and not with just a few years of shaping but with many many years experience on the water and in his shed
he knows his stuff
Ive been investigating this too,
You can get Mal blanks that are 3" thick (9'6"+)
and shape them back.
Im considering copying the tail shape off my surf mal but with more float under mast. (to make a lightwind freeride board)
the foam blanks come with pre spec rockers, and if your happy with a flat bottom then it wont be rocket science.
I think the hardest part would be routing in the mast and fin box, then glassing in. (plus correct positioning) - but again its do able.
There will be heaps on you tube of how to glass surfboards, so try there first. maybe use a heavier cloth around mast base, foot straps and nose.
the mast and fin boxes can be robbed from f*cked boards.
If i had more time on my hands I would definately go down this road.
yeah second what mark said about ecboards that was well worth reading a few times, Also I found this one useful.http://www.lbwindsurfing.com/raceboard/design-construction-longboard-windsurfer/
Took a bit of creative googling to find that, and also the Nelson videos on youtube.. Search for nelson factory custom windsurfing, get some popcorn on the go and enjoy..
This one is my second effort, prepare for lots of haters if anything on it doesnt look perfect..
regards the shaping, depends how good you were in woodwork in school..
Nude boards look like great boards that go really well but I don't think podium spots is an indication of how good boards are, great sailors can sail any old board really well. But if that's a factor what about Mark Stone he's making comp winning boards too, Jeager uses them.
or Mike AKA Decrepit down in Mandurah.
Any experienced shaper can give sufficient information for designing one's first board...so it shouldn't really matter :)
ecboards is the best one still on the net. This is the link to nelson www.nelsonfactory.com/en/the-factory/video1.php
A few more links
www.akushaper.com/
www.swaylocks.com/ (more for surfboards )
www.gurit.com/core/core_picker/download.asp?documenttable=libraryfiles&id=1119
www.surfboardbuilding.com/index.html
and if you want a real chaep board pages.infinit.net/endo99/board.html
Try to find some one local to help if you can and give it a go. Your 1st effort wont be the perfect board but it will still be worth the effort once you get it on the water. A lot of the material are toxic so stay safe on OH&S.
heres an old longreef express after removeing all the glass and reshapeing
, the way i see it is theres no point in making a board you can already buy,its funny, guys sailing sanctuary point for the first time see my slalom board and say wotthefrrrrk
Just copy other peoples designs - like you have with my avatar (from Boards & GPSTC!) 
It was a design I came up with a few years ago after getting catapulted by a downed kite, and think it works on so many levels.
Imiation is the most sincere form of flattery, I dont mind and would love to see stickers of it on all windsurfers cars
Oh I feel so disrespected and dirty PC
Anyone with the strong desire and a tiny bit of dexterity can shape and make a board I have a quote from Jimmy Lewis "copy a fast board use lots of measurements"
The difference between an awesome board and an average board is only under a couple of mm, the difference between an average board and a pig is usually 10mm plus. If you take your time and stick to your planned measurements you should get a reasonable board.
Understanding how the water will flow across the boards surface and how the tiniest of changes(less than mm's) will affect the board, will allow you to shape a great board. But until you have this knowledge of water flow from the experience of shaping and sailing many many many boards, copy a board to the mm from a very experienced world class shaper. Like most projects the planning/preparation(taking measurements and marking them out) would be the most crucial part.
I made my first epoxy sandwhich boards with the most basic equipment eg I bought 2 second hand vacuum cleaners and swapped them every 45 minutes during the vac bagging process. Go for it, there is heaps of info on the net these days you just have to put in the time to find it and absorb it.
One day when I get some time I will make up a step by step website on how to make a board using the most basic and budget equipment.
Oh and thanks for the compliments DTL
after a few modifications
keef i have a glass board i could slightly reshape move mast track foot straps whats the easiest way to strip off the old glass & can i glue in the cut off nose bits into old holes ? thanks max
actionmax im not sure if the polyester glass will come off the same as epoxy but anything is possible,a lot of old glass boards had plastic US boxes and mast tracks, but if your not going to use the board and you want a bit of shaping practice you have nothing to loose , do you know the volume and length of your glass board
too take the glass off you just need to use a router on the bottom, say 4" either side of the center line and score the glass, then with a Stanley knife carefully cut through to the glass, it should pull off with just a fine even layer of foam, just keep on going over the whole board with the Stanly knife
after you have reshaped you will need to give the blank a light layer of micro balloons
, if you decide to go a head with the project start your own post and see if there are any professional guys out there that are experienced in pollster boards ,and how easy the glass will come off
yes you can use foam from the nose to fill in the old mastrack , to do that just use some spray contact adhesive, don't use resin it's to heavy
Hey PC Yes it worked the board felt very much like a quad it trucked upwind, had a skatey feel and had more grip in the top turn and feels like it turns smaller arcs than the twin, but I have gone back to using it as a twin at my local, I just prefer the feel as a twin with big fins in cr4py cross onshore conditions with that lovely side current.
