To view the room in Hammer, go to View - 3D Textured Polygons. Then move your cursor over the 3D view, hit the "z" key, and then you can fly around, just like noclip. Hit the "z" key again to get out of the noclip mode.
Maybe a reason your room didn't show up is because you didn't make it hollow. To make it hollow, select the block, go to Tools - Make Hollow.