Thanks dude, Managed to sort it eventually, just broke the selection down to smaller chunks and combined seperately, must of been some kind of system limitation that was freezing me. Strange i should get areas with zero map area though, i gave up on extruding faces for that particular problem, i tend to prefer extruding edges now, i'll only use extrude face in the very early stages and for inlets or anywhere that i'll be shrinking the face from its original boundaries.