you looking for trouble?
a home made bathub? does the thought of a leak scare you? what about 10 years from now? 15 years?
i dont think youll find step by step instructions, so you have to follow the rough steps i shall give you
you would have to frame it out, rough the plumbing, put the shower pan material, then some chicken wire mesh, thin-set cement for general shape, then lay your tiles and grout, finish off the plumbing and hope your homemede tub dont leak or all your work is for nothing
you doing this yourself?