Don’t expect a home made machine to be anywhere near to what can be achieved using expensive commercial machines manufactured by big engineering companies; but if you are the adventurous type and like to do things by yourself, there is not reason you should not build this machine. Since CNC machines are used to perform any number of tasks, you need to ask yourself what your home made machine would be capable of doing.
Obviously you have to set simple goals e.g. you cannot say that my home made CNC should do all the household work, fix all mechanical problems in the house or go to pay your bills. I mean you could dream that big, but that would certainly require a much more knowledge that I could give you. As for the rest of the humbler folks feel free to read ahead.
We all like to engrave things on wood, plastic or metal and so one of things that you can expect your home made CNC machine is to do some simple two dimensional etching for you on such materials like plastic or wood.