Building an Arch

This tutorial will show how to create a basic
arch and to match up textures effectively.

Making a decent arch can be a little tricky.  You'll need a doorway
to work with so if you don't, get crankin'.  Create a brush that is the
same size as the opening of your door.  You'll have to edit the brush
anyway so you don't have to be too picky about it's size just yet.
Go up to your toolbar and with the brush still selected choose the
'curve' option and then 'end cap'.  You should see an arch outline
within the brush.  For some reason all patches such as endcaps,
cones, cylinders, ect. are created facing the ceiling of your map.

   

This means you'll have to flip it over by using the x-axis rotate button.  
Once the brush is facing the right way you'll want to line up the red
bounding box of the patch with the door opening.  You can make it
as long or short as you like.  Use the image below as a guide.

   

You'll notice that the corners of the arch are still open with 
an absence of any texture.  It's time for a cap!