All you need is a blue long piece of fabric or a sheet and some golden rickrack. Just drape the fabric over you like you would a toga and let it hang about floor length. You can pin it or sew it. Take the rickrack and wrap it once or twice around your waist and then wrap it in an X across your chest up to your shoulders.
It would give it a nicer touch if you could make an X on your back too.
Some nice Roman effects would be gold costume jewelry. Use a gold necklace or pearls and put them on your head.Also, what I use, is tulle fabric with flecks or gold in it as a shawl. It looks really good!
Thanks to Jenny for this enchanting idea!