Let's make a flying buttress. What's a flying buttress?
you ask. It's a supporting arch.
Looks something like this.

They are easy to build and look cool in a gothic map.
The first thing to do is build the trim brushes on the
walls with which the bent cylinder is going to connect.
These are just square brushes that have the front side
moved (E key - edge edit) so they're are angled.
Next thing to do is build the square cylinder and bend it
into a arch.
Let's build a brush 40 by 40. I used grid 8 and then built the
brush 5 grids by 5 grids.
Now turn it into a square cylinder, (switch to top view
then curve menu then more cylinders then square
cylinder.)
Now go to the side view (x or y) then turn on vertex
editing (V key). Now we are going to position the
control points.
A fast way to get them close is to left click, hold
away from the points, and drag a blue box around a row of
points. Now release the left mouse button, left
click on the points themselves, and drag them close to where you want them.

Now they are
close.

Now move
them into position. Notice I had to snap the control points
to the grid (ctrl+G)

Now that looks good for now.
Let's build the rest of the brushes to finish this flying
buttress off.
This is how I do it. Build a brush above the square
cylinder that we just bent in to shape. Texture this
brush with the common/caulk texture.
Now turn on edge editing (E key). Let's turn this
brush into the top of the flying buttress. I made it
wider than the bent cylinder and shaped it like this.

Now let's build the center brushes. These are going to be
narrower than the bent cylinder. The reason they are
narrower is becaue they'll be inside the cylinder and so you
won't see any z-fighting.
Here is a finished pic with all the brushes selected.

There now all that's left to do is to texture the brushes. I
used gothic_wall/proto_brik for the middle brushes and
base_wall/rusted
for the top trim brush. Make sure you caulk all unseen
faces. If you made all the brushes out of caulk in the first place and only
textured the visible surfaces, then the job's already done for you. Tip hold down ctrl+shift+alt while
left clicking on all the faces to texture sure saves
time.
Do you want something else covered by this Mesh Tutorial
then write me a email.
Email Bill Brooks
Bevel trim