Most designers wants a fee for each boat built. Something to check with the designer when getting the plans.

As to saving money.. Unless you have done it all before and have lots of contacts to source parts and materials really really cheap, your homebuilt boat can be even more expensive than one you buy. Especially so if you buy a used boat! Buying a used boat is the most economical way to get a boat unless you really get into sourcing parts on the cheap and have the industrial contacts.

There have been lots of discussion about this before, some searching should give many interesting posts making just the points Wouter made.

E.g. ref: http://www.catsailor.com/forums/showflat.php?Cat=0&Board=Fleet45&Number=60234