I would suggest that even the simpliest boat design takes a serious investment of time and money to build. Almost always you can buy and restore a similar sized boat for less than it costs to build one. If you intend to build a boat, then the process of building needs to be a labor of love and not just an imagined economic measure.
And if you are going to build a boat, then I would respectfully suggest that you pick the best boat design that you can, even if buying the design is considerably more expensive because even a seemingly expensive set of drawings represents a very small portion of the cost of building a boat. And with a good design you will end up with a good boat that has some real value at the end of the process.
While many of the historic designs are fun to look at and nearly free, these boats are very expensive and time consuming to build, are much higher maintenance, and require a wide range of archaic skills and hard to obtain materials as compared to the better designs for modern wooden construction. There are inexpensive sources for designs like GlenL and Roberts, but by and large their designs are dated. A huge amount has been learned about hullforms and building techniques in the past 30-40 years. This results in boats that are easier to build, and which are more seaworthy, comfortable, and sail better. If you are only building a very simple boat then Glen L and Roberts are probably not the best way to go.
Many of the top design firms in the world offer designs for amateur builders. Firms like Van deStadt and Farr for example offer a number of very nice 25 foot designs. There are also firms which specialize in designs for amatuer builders. Of these, personally I like the work of designer Dudley Dix. Boat plans, yacht designs & boat kits from Dudley Dix Yacht Design & Boat Plans
His work walks a nicely balanced line in terms of being creatively conceived, technically sound, and with details which are well thought through and clearly documented.