Goodday Robi,
Firstly you aren't crazy, it is more than possible for someone with a fair aptitude to building things to create themselves a very good boat. I've done a bit of amateur boat building in the past and like you am interested in building myself my next boat. There's plenty of web sites around with ideas to explore if you can use a search engine.
Depending on what you want to build there's a few ways you can go, if you like to race then look at the formula classes where you can make up whatever design you fancy if it fits in the rule then hey presto you have a boat with a racing yardstick! These include F14, F16, F18 and A class boats, I believe you can also get building plans for the Tornado, Taipan 4.9, Blade F16 and Mosquito.

As Mary inferred, some people just get off on building things so don't worry about the knockers, though they do have good points and your aware that If you create the worlds slowest F16 then it probably won't sell for more than firewood (but as long as you enjoy it and built it to last a long life then you'll get more in enjoyment than cash.)

Cheers Phil


ps keep us informed of your progress if you go ahead.