Re: Making An Arena Mode Map
A few notes:
Make sure Snap to Grid is always on and try to keep the 1024 grid in mind, make your individual areas in 16 unit increments within those 1024 sectors.
Decrease the size of your grid for detail work but leave it at 16 units most of the time.
Not everything needs to be at least 16 units but radiosity in the Source Engine will behave better.
Where light bleed and weapons fire aren't a concern floors and walls can safely be 8 units thick.
Try to never make any brush thinner than 1.0 units, other than in special cases like illusionary glass for layered viewing effects.