Thank you Bazzwano for youre response i understand, but how do you add vertices to make a curved ceiling for the hall or add vertices to the sides.
you mean for my example? im not sure what you mean.. well in the geometry editor, there is a mode that will render the sides of your builder brush (making it look like a red block), i forget what this mode is called, when you open the advance options diolog on the geometry tool you can click a surface and extrude.. making more pollys. I personally dont do this.. if the vertex's for my shape is on the grid ( my BSP is mostly square shapes) then i would just place a new brush next to it, that way its more editable, because once you make a polly Iv found deleting a Polly makes holes. that may not be what you want.
you can consider creating a spher and cutting it in half..
I would like to point out. the the BSP for all my maps is very simple.. i suggest you have a look in the editor so see that you dont need to make complex BSP to make a good map. in fact its a very bad thing to make complex bsp.. thats what meshes are for.
if there is a particularly shape you wana make but dont know how.. then ask