Cut slope 1:1 for foundations.

Hi,

I have a question regarding on how to create a cut for some isolate foundations (square shaped) with a cut slope of 1:1. So far I have tried to draw a square, assign an elevation and then apply a linear template but it can not create the 'hole'. I want to determine the volume that need to be excavated for that cut. 

Thanks you in advance. 

PS: I am sorry if the question sounds stupid, but I am quite new to PowerCivil.