First, you need to make sure that you have the right conditions for the construction and maintenance of an aquaponics system.
Space is the most important factor to begin with. An aquaponics system needs room, and a good minimum size to allow is four cubic feet. This should allow enough space for a 100 gallon fish tank, a 10 inch deep growbed, and the room to work in and around the system. This may sound obvious, but remember: the bigger the system, the more space you will need.
Of course, if you are designing a simple mini-aquaponic system (like this) with a small aquarium feeding directly into a supported growbed, then the amount of space you need will be vastly reduced. The key is to plan accordingly.
Sunlight is probably the most important factor after space. In aquaponics, the ideal sunlight configuration is full exposure for the growbeds, and reduced exposure for the fish tank.