Creating Solids from Scratch
Creating solids is quite simple. The process always follows the same four basic steps:
Select the Block tool.
Note: The arch primitive is a special case. It is not actually a primitive object, but an Arch tool which allows you to quickly and easily make multi-piece arches. For more information on the Arch tool, see Using the Arch Tool.
Drag a box in a 2D view, making sure it is the correct size and in
the correct position in each of the views.
Creating Solids by Cloning
Cloning provides a simple way to quickly duplicate an object or group of objects. This includes both brushes and entities, and groups can contain a mixture of both.
Go into Selection mode by pressing Shift+S.
Once you have a prefab library created (see Creating and Using Prefabs), it is a simple task to insert a prefab into your level.
There are two ways to put a prefab into your level.
The simple method is, from the New Objects dialog, to select the prefab library from the Categories selection box, and the specific prefab from the Object selection box, and then press the Insert original prefab button. This will insert the selected prefab in the center of the 2D views. You can do this with either the Selection or Block tool selected. Simply move it around into place. (Make sure Texture Locking is turned on!)
The second way to insert a prefab is with the Block tool. Press Shift+B to go into block mode, then create a box the same approximate size you want the prefab to be. Select the prefab library and prefab object as described above. Now press enter to create the prefab. This will create prefabs at any size you specify, rather than inserting them at original size then requiring you to resize them manually.