I designed mine with that in mind. I can reach the fans, the lights, and the window without any problem. I don't have room for a Topside Creeper, which is a great piece of gear. We have one at the museum. It is not designed to stand on, which you might have to do in order to reach the ceiling. It also takes up a lot of room and you have to have three feet or so of clear space under the layout to accommodate the frame.
Some people build little platforms that can be set in place over track or a parking lot or something, that you can kneel or stand on for access to the ceiling or interior parts of the layout.