Right, so I said limit one ad per customer but since the money's already been transferred I'll change the rules to something a little more sane.
Limit of one ad per customer has been removed. Ad tiles (including the two 256x512 tiles for LW) can either be combined to form, for instance, a 512x512 tile, or separated into two distinct ads. The back wall will be used for ad space as well if more than 12 ad tiles are purchased.