if you want something more custom check out the TEENSY which is has lots of examples and code for making keyboards.
use a drawing or CAD program for the switch layout then cut it with hand tools using a guide or send it to a LASER cutting service for a more zact end result. in my experience Adobe Illustrator will work just as good as a CAD. Wood, MDF, plastic, or metal are all materials to consider for mounting switches. and it does not really matter what as long as the keys snap in place.
before you embark on a keyboard build consider there are many existing keyboards that might fill the bill in terms of ergonomics or customization.