Built my own Sea kayak not too long ago. Depends on the boat design you go for, but if it's wooden then there's loads of crossover techniques. Mine was stitch and glue (Okoume Marine Ply, Epoxy, 2pac varnish).
Takes ages, but you really do get satisfaction with the finished product:
I've been out in some pretty nasty seas since, so it's had a good pounding, and it's a great little boat (18ft).
I'm reasonably handy with wood, but no expert by any means whatsoever. If I can bodge it together, most people can. I had to build a 23ft shed to build mine in first! And it got varnished inside the house (good job I had doors between the living and dining room!). Missus wasn't impressed about the varnish on the new sofa though - but since she was the one that spilt it, I got away lightly.
You'll need to become one with sanding - find the zen of sanding - you'll be doing more of that than ANYTHING else.
Usual stuff though - measure twice (once more for good measure), get a mate to agree, get the wife to agree and then cut. Can't be your fault if it's wrong then, and if it is then you'll not get berated for buying new timber
Best of luck if you do go for it! Just remember you need somewhere to store the bugger after!