This does sound like a problem. Roses should be putting on a foot or more of new growth after pruning. You mentioned they were on the hot or South side of the greenhouse. Perhaps lack of water on hot days contributes to the problem. Is the greenhouse new? Did you damage roots putting in a cement foundation? If the roses have never bloomed well even in prior years that tells me poor soil, lack of water or even a viral infection may be adding to the poor performance. Sometimes the best thing to do is give up, uproot the roses and plant sedums, succulents, salvia or rudbeckia daisies - all plants that would survive heat and poor soil. Keep growing, Marianne Binetti