Complex sentence: The mall's layout consisted of a two level, open-middle, long rectangle shape, however, by having no main roof over the mall, walking from store to store put you outside in the cold during the winter months.
Split into simpler sentences: The mall's layout consisted of a two level, open-middle, long rectangle shape. However, by having no main roof over the mall, customers were forced to walk outside to get from store-to-store during the winter months.