Decide whether you plan to transport your outdoor tent canopy from place to place, or will leave it in a single spot. If you plan to move your outdoor tent canopy regularly, consider its weight, and whether you can lift it into your vehicle easily. Also consider its size, and whether you can fit it inside or onto the roof of your vehicle.
Consider whether the outdoor tent canopy will remain standing or periodically taken down. If you plan to leave it standing, choose a sturdy design, one that can withstand ongoing exposure to the elements. Larger, heavier tents tend to be sturdier than smaller, lighter models. If you will be taking down your tent regularly, choose one that is easy to set up and break down.
Check different outdoor tent canopies for accessories that come with the initial purchase. If it is important to have an awning or side walls and you don't want to pay extra for them, choose a model that comes with these extras. Don't choose a tent solely on the basis of additional amenities--you can always purchase them separately if the model you want doesn't come with them--but do weigh their presence or absence into your overall purchasing decision.
Investigate whether you can obtain replacement parts for your tent. If it is a well-known brand, or if you buy it from a dealer who specializes in outdoor tent canopies, finding parts for minor repairs will be much easier. If you are unable to find replacement parts, you will have to replace the entire tent much too soon.