ok first off... dont make your stairs straight from a texture, use caulk and then texture the sides a player will be able to see.
ill make a set of stairs for ya..
so like i said before, start out with a caulk block about as big as you want each step to be or making the shape and size of your step. Im just going to do a basic step.

Next texture the faces which can and will be seen in-game.

(im using textures from trak2 and trak3 for this)
and now select and copy this 1 step and move it up and over.

repeat until number of steps wanted is reached.

Now for a wall, using caulk again, make your wall.

Now im going to use the cliping tool to chop it to a better fit.

Hitting enter will cut out the section i want or you can hit shift+enter to split the 1 brush into 2.

Now im going to use the clipping tool again and shift+enter to make this a little more detailed.

The after result, 2 brushes from 1

Time to texture it.

Now you want to copy the wall and do an x-axis flip and then 2 z-axis flips.

Now you have your stairs. You can mess around a lot more for a better feel. Some stairs in my current map in-game:




Hope this helps you out.