How to lay a cement block shower? By using 3 blocks by 3 blocks by 3 blocks?

Are you also building a custom shower pan or using a preformed base? Why so small, this will end up with almost no elbow room less than 30" . How to Build a Shower Pan (http://hoagy.org/house/HowToBuildShowerPan.html)

You don't give many details, or why block, but I agree with the above post and think you should make it larger, If you have the room.

If this is just a DIY project, I would neatly stack the blocks, in the size you want, staggering the joints as you go up and at 4' high, stop, put a rebar in each cell, sticking up about a foot and fill the cells with concrete.

Now do the same thing to 8' or as tall as you want the shower and repeat the rebar and concrete filling of cells.

Now you proceed on and finish as you wish. Hopefully you have installed the plumbing inside the block, somehow, before you grout the block, ditto on the drain?

Write me if you need more detail

Good luck

Roger