i make it a rule that i finish the quilt all the way before i start another one otherwise i would have them laying around and my sewing room is not that big i would suggest storing it like you would a finished quilt if you fold it unfold it every once in awhile so the folds dont become permanent
i bought some nice bags from clotides with a zipper in them and it is made of a breathable material to store quilts in i just take them out and refold them every once in awhile