If you are planning on building a female mold then you would need to devote a lot of time, effort and money to do so. You would also need to be doing it with the view of going into commercial production to recoup your start up costs of the molds. Much cheaper to just go and buy a boat that meets most of your criteria. If you are primarily after a wide beam for the length I would advise you to go and look for designs for a catamaran based hull.
As a one off boat for yourself, there are plenty of places you could get the plans for building one ranging from Wooden, GRP, Foam sandwich and Aluminium.
But you need to be aware that there are lots of start up cost involved before you could even begin, some of them are:
1) Place to build it.
2) Tools
3) Plan costs
4) Good building skills for the type of material you are working with, if Aluminium, do you have experience welding it, do you have a good welder capable of welding Aluminium and I don't mean a welder from the likes of Bunning etc.
5) If Fiberglass, will your neighbours or council prevent you from building in the suburbs. Do you have lots of experience in laminating GRP. Noise factor from grinding. Whilst anyone can laminate with some basic instruction it is also so easy to stuff up the boat if you don't have good experience. I used to repair boats for a living and some of the major stuff ups I have seen are unbelievable by people taking shortcuts or by not really knowing what they are doing.
A lot of people do build boats for themselves but it is not a cheap process in time and effort and more importantly money!
So you got to ask yourself do you really want to go through all this for a one off boat?