A shield is a kind of defensive weapon. Held in the hand, it is used to deflect sword blows or projectiles. Shields come in a variety of shapes. They may be rectangular, oval or round. A round shield is often reinforced with a metal rim that can be used as an offensive weapon. The user of the shield strikes opponents with the rim.
Trace a circle onto a piece of plywood. The circle should be 2 feet in diameter. Cut out the circle. Mark two points on each side of the circle just above and below the middle. Each of these points should be 1 inch in from the edge of the circle. Glue a leather strap between two points on each side of the circle. These are the handles of the shield. The handles should be long enough to comfortably accommodate your arm.
Bend the metal shelving bars to the circumference of the shield. The shelving should clamp over and completely cover the outer edge of the shield. Attach the shelving with plumber's brackets. Use as many brackets as will make the rim secure. Bolt the brackets in place.
Stretch a bicycle tire over the outer rim of the shield. The diameter of the bicycle tire should be slightly smaller than the diameter of your shield. The tension of the tire will bend the shield into a slight dome shape. Assist the process as needed by pulling inward on the shield handles. You can steam the plywood to get out any unevenness.
Bolt a hubcap to the outside of the round shield. The hubcap should go exactly in the center. This will be the boss. Paint the shield in whatever designs you think appropriate. Paint the boss or incise it with a metal cutting tool or awl. Remove the bicycle tire if you would like to make use of the shield's hard edge.
TL;DR (Too Long; Didn't Read)
Modify your round shield by cutting notches in the sides. These notches can accommodate a spear. You can also cut longer indents in the sides to allow for better swordplay. Try boring a spear hole through the center of the boss.
This is a light shield. It will not protect against heavy weapons or bullets.