The -15 is my first boat build too.
I read about 500 webpages on wood choices for boat building before I bought a single piece. I should have spent that time building instead. After you read about three pages you will have a short list of good candidates and a long list of "never use these." I think you can really distill wood choice down to price. I will be painting most of my boat, so the frames won't show all that much. Looking back now, I would think about the length of time you are going to own this boat before you get the itch for something bigger, and how much you want to spend to build it. I would have found (relatively) cheaper wood and spend big on the exposed parts. In the beginning I thought that I would poly/varnish/clearcoat the who inside, but as work progressed it became clear that I should cover as much as I could with paint. The guys over in the powerboat forum have some really nice looking boats. It also took them Y E A R S to build them. I know it's a "labor of love," it is for me too, but the sailing is much more fun than being covered in sawdust as you make that @$!% part for the fourth time so it will fit just right.
Anyway, heres my (short) experience.
My frames and whatnot are "real" Honduras (?) Mahogany and they cost me about $1,400 so far. I do have some leftover, but will need more for the seats, floor boards, splash guard, CB trunk cap, etc. (You know, all the stuff people will actually see...) I bought 7 sheets of 6mm (1/4") Austin (manufactured in India)(??) HydroCore plywood for $350 plus freight. I think I could have gotten away with cheaper stuff since it will be encapsulated (buzzword here for "coated") with epoxy to make it waterproof.
After reading the first three websites on wood for boats I should have just bought what I thought was most cost effective. In the South you can get SYP (southern yella' pine) or white oak for reasonable and everything else is spendy. SYP is junk wood from my reading and oak don't take too kindly to epoxy. I narrowed my list to Mahogany (expensive = Phillipine, outrageous = Honduras), Spruce, CVG fir and Cyrpress. Cypress is still cheap (relative) but was too much work to track down. Asking for CVG fir at the lumber yard got me a few blank stares. This was a well stocked lumber yard too, not HomeDepot of Lowe's. Spruce was special order since it grows mostly on your coast up into Alaska. So I bought the most expensive rough cut Mahogany I could find and went to work. Looks really good until the changing humidity and kiln dried nature of the wood made it warp and split in funny ways. That caused a lot of waste as I tried to re-saw a straight piece out of the mess. I think I have thrown away half of the wood as sawdust.
If I build another -15 I will try to buy as much wood, plywood, etc. at HomeDepot or Lowe's as I can. Use the savings on the bronze screws (Glen-L's fastener kit is the best price around) and extra coats of epoxy. I would also build it faster so I could enjoy the fruits of my labor. I know you can't (read: shouldn't) rush this sort of thing, and I may be in blasphemy territory here but I know I stressed out about many things that were way too small to matter. My dad built a boat when he was 16 and used Mahogany that came to a total of something ridiculous like $57.26. It took him a month of afternoons and he still got his homework done. He sailed it on the SF Bay (I'm a native Californian, stuck in SC against my will) for three years before he sold it to a guy who bought the boat because it came on a trailer, and he really needed a trailer. If my son (2) ever wants to build a boat over 10 feet long, I would tell him to buy one. You'll be on the water quicker, there is always something to fix anyway and I would bet you save money and headache. Even if it took me 10 years to build a 15 foot boat it will never match the precision of a mass produced fiberglass dinghy. Wood looks and feels good, but do you want to look good or go sailing? I can't wait to finish my build so I can get to the good stuff.
All advice is worth listening to, even if you don't follow it.
watch as I attempt to build the Glen L - 15 @http://www.stevesboat.blogspot.com