Create a pattern after determining whether you want a shield that is circular or rectangular. If you are making an oval or a round shield, you can make it from wood, but making the pattern from a heavy cardboard might be easier to begin with. If, on the other hand, you prefer a rectangular shield that will mold more closely to your body, use a thick cardboard to begin with so it can be bent around you. Most shields in this time were between 3.5 and 4 feet long and 3 and 3.25 feet wide. Stick a nail in the material you're using, near where you want the top to be. Measure 3.5 feet down and add a second nail. If you're making a rectangular shield, you have your top and bottom, but if you're making an oval square, it's not so easy. Take a string that's almost double the length of the distance between the nails and tie it to each nail. Then, take a pencil and draw a line extending the pencil the width of the string on either side. This is not easy, and may take several tries, so don't be discouraged and keep the pattern in case you want to do it again.
Cut out the pattern and move it to the material you want to make your sword from--be it another sheet of cardboard or a wood board--and cut that out. Reinforce the back of the shield so you will have something to grip that won't break. A crossbar works well. Sand the wood beforehand.
Cover the roman shield with a leather, canvas or cloth substance. This will make it look more genuine. Fasten it with rawhide, metal or leather so that the cloth will stay on. Use staples if you really want to, but they will detract from the accuracy.
Paint your shield in bold, bright colors. If you have a family crest that you know of, this is perfectly appropriate to paint onto it; if not, use a simple design or pattern of your choice.