I use GTK Radiant 1.4 ( the best ) and I need circle walls to my map, walls that I can add a gate to it, yes it will be a map of Minas Tirith. I have one way to make em, but it doesnt satisfy me.

Do you mean you want to know how to place a vent hole in a circular surface? I'm sure there's ways you could do it with multiple patch meshes, but matching the edges up without any gaps is going to be quite hard. (At best.) Although, the whole thing could probably be built geometrically and phong shaded to make it appear curved.

Eh? Speak english, mate! Anyway I have done it with using curves -> belve (or something like that) and then thicken and made 4 times that and it makes a circle where I can add a gate and towers without putting em into wall.