1) First start off with a room that is 5x11, 8 clicks high. Next select an area of 5x5 and slope it 1 click. Use this pic as an illustration.

2) Now, select another area (circled in red) 5x5 and slope it once just like the other side. This time, however, move the slope one click lower than the first.

3) Next, select the little 'isle' highlighted in red (below) and slope it so that it matches up with the second slope circled in red (upper right) that you created. Now slope the 'isle' again, but this time so that it matches up withthe other slope.Your room should now look like this.

4) With the 'isle' selected, raise it four clicks to look like the picture below. Then, click the wall button and texture it according to your tastes. With all these things in mind, you can stop one of the worst disasters from happening to your level.