Sure, you can get pretty creative with the doors. Generally you want them to allow easy access to the tank so front opening is often best. Sliding doors are popular, but you can use ones that have locking hinges and open up or open down, or you could have them open outward with hinges on the sides. Just as long as the doors are stable and can be latched you can configure them however you'd like. I personally like doors that latch on top and drop down out of the way. I currently have doors that have hinges on the side and open out like a cupboard but I wind up bumping into the glass a lot of I leave them open.
