I have a composition that calls for a very wide and very long floor that fades off into the background.
I created a new 3D solid and in the initial dialog box I put 15,000 x 15,000 pixels for the solid size. Of course, I quickly found out that after applying a few effects, AE gave me a "out of memory" message. Obviously creating solids that large isn't the way to go.
Is there a more practical way to create an extra large floor area?
You might also try tiling with an effect, though I'm not sure off the top of my head if that will help or hurt the processing requirements of your comp. Create a smaller solid to start with and use CC Repetile to extend the edges as far as you need them to go, and see if that works any better.