It depends on what you consider to be the "front" of your Lot. If you consider the malbox and trashcan to be the "front," then Floors may appear to be rotated differently than how you would expect. Custom content Floors appear in the same orientation as The Sims 2 Floors. For example, wood floors with slats that are horizontal in the thumbnail, will appear vertical when placed on a Lot (with the mailbox side as the "front").
Question and answer provided by the official FAQ