Principal, it depends on what type of boat your wanting to build. Most kits are to make a wooden driftboat. You can google it and a few makers will come up immediately.
I work with a guy that build his own drifter. It is sharp, he has had it for several years and just recently remodeled the interior and put a new HDPE bottom on it.
Boulder Boat does make a kit that allows you to assemble one of their HDPE boats with trim.
Don't know of any aluminum or fiberglass kit makers.
You can't depend on your judgement when your imagination is out of focus. - Mark Twain