You can create unlimited prefabs of your own design for quick and easy insertion into any level. The way you do this is to create an area you would like to replicate and save it to a PWAD. If the area is an existing level, highlight the area by selecting the lines (or sectors) and press the Save Prefab Buffer tool bar, select from the Prefab menu or press Ctrl+F3.
After you have created the prefab PWAD, you can enter it for repeated quick entry as a User Prefab by selecting the top Prefab menu, click Change Prefab#, enter the number you want the prefab to be and supply the name in the dialog that comes up. You can make up to 20 quick access prefabs in this manner.You can change them at any time.
The first 9 can be quickly accessed by pressing Ctrl+1 (1 is from 9). The others can be quickly accesses via the Prefab menu.