You should first complete each of these steps with cheap fabric to ensure the correct fit. Measure the distance around your hips.
Belts can close at the back, front, or side.
It depends on your design. Make separate front and back pattern pieces. The angle at which you make the side seam can help contour the belt for a better fit. Making 2 small darts at the center of the back piece will also help. Sew the belt together, placing clasps on opening.