Time to create our first room, something we can actually run around in. Save your work, create a new file, and save it as DM-CSGTest03.udk.
We want our room to be big enough for the player to run around in. The builder brush is 256x256x256 by default, and the player is 88 units tall. That's going to feel a little cramped, so let's make our cube more like 1024x1024x512 units tall. What we're going to do is create an additive cube which is the size we want, and then hollow it out by using a slightly smaller subtractive cube. Select the builder brush and make sure you're in the Geometry mode. Yes, the geometry editing tools work on the builder brush too.
Also, resize your grid to 32 units either by using the controls in the bottom-right corner of the screen or the bracket [ ] keys. It's important to build on the grid so that we have an easier time-judging size, and so that when we expand our level later, everything lines up nicely. This is also why we...