A suggested course of action for planning a layout:
1. Draw a floorplan of your available space. How big would be convenient for a layout, allowing for good access to the layout and other parts of the room, if necessary?
2. What kind of trains do you want to run? What is your idea for a minimum radius standard?
3. What kind of a layout do you want, and what kind of features? "Realistic operation", toy-train operation with multiple independent circuits, long mainlines, industrial areas with places to switch, less track with more scenery, etc?
4. What is your level of experience in model railroading and layout construction? Do you want an easy-to-built beginner layout or a more complex multi-level layout?
5. What type of track do you plan to use?
These factors are all relevant to consider first when planning a layout project. If you can spell out these parameters, you have a better chance of getting some input.