Adding halls to a production area by using GAMS?

Question

I have a grad project the topic is facility layout problem. I have an 75x95 sq meter area and I want to divide this area into 4 equal horizontal halls in order to allocation of the departments into these halls. There are 11 departments and 6 of them fixed (have predetermined locations). The rest of 5 is my decision variables in terms of length and width and space requirement. I cannot achieve dividing into halls and fixing the 6 departments which have predetermined locations. In GAMS how can I satisfy these constraints and definitions please help me. Thanks in advance. I defined 2 separate sets as fixed and unfixed departments. For fixed departments I gave length and width of the relevant fixed department (i) and the area of the department (i) as parameters. Then in variables I gave lower and upper bounds to length and width and area of unfixed departments. I wrote non overlapping and space usage constraints. I need your help about defining coordinates and dividing into halls.