Hi Ken --
If you can use Manage Content and Surveyor it’s not all that difficult.
If the layout uses dig holes:
Use Manage Content to identify the dig hole used in the layout.
Download “297 marker Tower”.
In Surveyor:
Delete the floor spline (it will run longways and there may be more than one spline).
Delete the invisible track spine to which the baseboard legs are attached.
Use the Replace tool to replace the dig hole with the marker Tower.
Save.
In Manage Content delete the marker Tower.
In Surveyor use the Delete Missing Content tool. Save.
You have now removed the floor.
If the layout uses terra-forming to lower the floor:
The fascias are splines. Delete.
Use the terra-forming tool to lift the floor height back to zero height.
The walls are splines. Delete.
None of my layouts use a ceiling. It’s a dark sky. In the environmental settings use the sky of your choice.
That’s the easy part.
The hard part is terra-forming and texturing what was the floor. You might have found the two versions of Yuan Gulch on the Download Station? One is a model layout the other is a route. In the latter I replaced the floor with a lake. That’s the easiest option, but it still needed quite a bit of terra-forming and texturing to give the desired effects.
_____
As for:
" ... i do not understand why so many people want to create model railways in Trainz ... "
Well, it gives me (us) a lot more creative freedom. Which for me makes it more fun. And I also discovered looking back at my previous routes that, all along, I'd been making model railroads but I'd actually been disguising them as real routes. So the decision and the transition to model layouts was easy.
Phil