I am installing ceramic tile on a shower wall and I am putting it a couple of narrow shelves using dried out treated lumber. My question is, do I use backer board on the sides, top, or bottom? Is there anything else I need to know?

I would not use treated lumber anywhere in a shower. It's too unstable for that application and will likely cause cracking grout.

There are a few other factors to consider to tell you what is best for your shower shelves, but you can certainly use one of the stainless shelves made by Innovis, or a prefabricated shelf like you can get at Lowe's or Home Depot. You can build your own custom shelf, but how you waterproof your shower may determine how you build your shelf.

I personally like the tempered glass shelves. They cost about $20 each at my tile supplier.

I generally use scraps of granite or marble counter top material. I get them for free from the garbage bin of a counter top place. Marble and limestone are far easier to shape and polish than granite, but either will work.

If you want to tile then shelves, then you should make a sturdy sandwich out of plywood and tile backer and then completely water proof it just like the rest of the shower.

It looks like I am going to install some ceramic shelves from Lowes which need to be glued on. Any suggestions on the best glue to use? I've heard polyurathene is the best. what do you think?

Definitely not polyurethane.

Are these shelves designed to be set into the tile or on the surface? If they have an outset on the back, then the tile should be cut out to allow the outset to go against the wall. For those, I use thinset.

If it's made to be stuck to the tile, I would probably use an epoxy cement. It's messy and you have to work fast, but it has a superior hold in wet conditions. You don't want those shelves falling off the wall, particularly while someone is in there.

Ok, thanks for your help.