I am going to be controversial, don’t go for a classic oval as unless you have loads of space you will find it hard to stop it from looking like a train set and being toy like. The best thing is consider what a real railway is? there are long and thin so go for a model railway on a shelf. I had one that was sat on a shelf about 12/14 inches wide around 3 walls. It was in total 29 feet long and with the help of a loop a the far end gave 58 feet of track, but the room could also accommodate being used as a spare room. It had a terminal station that had a run around loop, freight shed and sidings, along with an engine shed. The branch line ran down a slight incline disappearing behind the freight shed where it took a sharp turn out of sight and ran down to a junction with the main double line. This then disappeared into a tunnel where it did another sharp right turn and on towards a double track station, after which the lines went stacked on top of each other behind a wardrobe and around a loop which brought the train back through the double tracked station, and back to the branch line junction where you could go back to the branch station or stay on the main line which ran into the fiddle yard under the branch line station. It did have some scenery development done to it but most of this was to hide the sharp curves.

Probably quite obvious, but whilst i dont have a layout, but going to lots of local exhibitions lets you get an idea of what works and what doesnt for your own layout