Please, Please ... If you intend to build your own soccergoal, keep the dimensions to existing measures, a real net is usually much cheaper and better than a homemade. 
The measures of a net to a 5-a-side goal is 3 meters wide and 2 meters high, the depth is 1 meter at the top and the depth is 2 meters at the bottom

For a 7-a-side goal the only difference is that the width of the goal are 5 meters.