First, for construction of your shower, you should check out www.johnbridge.com and look in their 'Liberry'. There are numerous approved methods of building a tiled shower. The pan is not poured, it is shaped with deck mud which is closer to wet beach sand than concrete. The shower drain, if you build a conventional shower, needs to be a clamping drain. The receptor that holds the grate is adjustable in height because it screws into the clamping portion. This allows you to compensate for various thickness of tile and setting bed. When you say walk-in shower, are you talking about an ADA approved, curbless shower? If so, then you need to make the area where the shower is recessed from the rest of the bathroom to accommodate the required layers and waterproofing. You'd want the shower area to be recessed about 3-4", depending on the size of the shower to accommodate the required slope to the drain (minimum 1/4" per foot to the furthest corner). Yes, you need a waterproof layer, even in the basement.
My preferred method of building a shower is with Kerdi from www.schluter.com. the Kerdi system requires their drain, which is set so the top surace is even with the sloped surface. The drain piece is adjustable in height and x-y to allow for the tile thickness...a neat feature, and, it is square, so cuting tile to fit is easier than round. They have preformed pans you can tile, or you can use deckmud like you would with a conventional shower. If you use this, it is fairly easy to make the entire bathroom floor waterproof so it won't wick up into the walls and mess with your framing. You'd use Kerdi in the shower, and DItra on the rest of the floor.