I happen to live in an apartment right now and I have the same amount of space in the same shape (except it is 9' along one wall and 5' long the other) This space allows me to have a branch line switching layout. I am modeling northern Ohio between Sandusky and Toledo, Ohio, south of Lake Erie. The 5' side is 1' wide and serves as my "staging" area (fiddle yard actually). This is where consists are made for a class 1 RR (Chessie, Erie Lackawanna, Pensy, etc) to deliver to the setout track for an industrial corridor, which is on the 9' side. My free-lanced Toledo Erie Central (TEC) takes over the sorting and switching duties from there, serving some 5 or 6 industries. At the end of the day, cars that are outbound are switched to the pickup track for the Class1 RR to pick up the next day. The industries are large (brewery complex, grain elevator), intermediate (manufacturer of small auto parts) and small (coal/fuel distributor, team track, etc.) so there are plenty of switching opportunities.
The "story" is that this is the mid to late 70's and it is the beginning of the deregulation/Conrail era. The industrial corridor is a small segment of the former PRR/N&W trackage that was going to be abandoned, much to the chagrin of the local industries. So, the local industries got together and bought that segment, worked out a deal with the (Class 1) railroad for delivery of cars and formed their own RR company to serve their businesses: the Toledo Erie Central. The "company fleet" consists of one EMD SW900 and one caboose. The offices are housed in the old but small depot, there in West Sandusky, a fictional town, which would be west of Sandusky, Ohio and east ot Toledo, Ohio.
It is this kind of a scenario that you can use your imagination on to put together your own version of the ATSF segment that you want to model. Remember, it's all about having fun, so let your mind wander and take a ride on it to your favorite railroad destination!