The more sunlight on the surface of the growbed the better, as this will allow your plants to flourish. However, although fish also fare better with access to light, it is not advisable to place your fish tank in direct sunlight. This encourages the growth of algae and other surface dwelling aquatic plants. This is undesirable, as it will remove precious oxygen and nitrites from the water, inhibiting fish and plant growth.
So plan to build your aquaponics system outdoors, with access to direct sunlight, or indoors, preferably next to a south-facing window.
If you do not have access to direct sunlight, don’t worry. You can purchase grow lamps which will serve just as well: but be aware that this will increase your running costs, and becomes less feasible for larger systems.
Other factors to consider are proximity to a power outlet, for the water pump (and possibly grow lamps); and temperature, which will affect the growth of both your fish and your plants.