The last rods I built up retailed for $110.00 each, I bought the same blanks and materials and built 2 for a total $130.00.
Not a huge saving, but better than a poke in the eye, plus my daughter has the pride of being able to say that she caught something on her rod that she helped me make.
However, if you were doing it because of cost alone, you are not going to be in front by a great deal, especially when you add in the time factor.
If you get a bit of enjoyment out of doing something for yourself, then give it a go. Each to their own I say.