I am custom building a tile tub, how do I install drain fixture? Also, do I need a shower liner or can I tile directly to the wood frame?

The best advice I can give to you is to ask you to read this. How to Build a Shower Pan

If you are building a own sunken tub than you probably have to Hot Mop it. It is too deep for liner. You have to buy specific drain designed for these types of tubs.

Having reread the posts I am confused, are we talking tub or shower?