Oooo...Ooooo..I know this one!! Make a brush the size you need, then cover it or actually make it a system CAULK-NON-SOLID brush. Then look for the forcefield texture and apply to only one side. The side you want to see obviously.
Now you want to see the outside of the map like the deathstar or just stars? Copy the brush you just made and put it just 3 to 10 units behind the FORCFIELD brush. Just slightly behind the other brush if you will. Except this brush has to be solid. This part might even be the outer SHELL of your map...so just put STAR textures on it....Voila......
My kung fu is also very weak