The Romans were the creators of Western Civilization. Without their influence, religion and armies, much of modern-day Europe and North America would be very different. The Roman army was a force to be feared and respected worldwide, and we still use Roman war tactics today. One of the things that made the Roman army successful was body armour.
Begin by preparing your welding equipment, forge and lathe. If you do not have these materials, or the expertise to work in them, you will need to hire professional help and provide them with the plans of the armour you wish to build.
Measure the circumference of your arm from shoulder to elbow, every 2 to 3 inches from the top of your arm down to the elbow. You will be using these measurements to create the metal "plates" that will make up your armour. Allow at least one inch for attachment of strapping material and the free movement of your flesh.
Measure your torso from the armpits down to the top of the groin about every two inches, as that will be the width of the bands of steel you will be making. Write the measurements down. The idea is to create an overlapping layer of metal "plates"---almost like the bands of an armadillo. Again, you will need to allow about a half-inch in the front and the back for strapping materials.
Cut your steel pieces to the measurements taken. Each strip should be at least 2 inches wide. Fire up the forge, heat your pieces of metal, and shape. This may be done with a metal forge and hammer, then carefully tested against your body once cooled. You want it to be form-fitting, but not too snug. Buff the finished metal edges to take any sharp edges off.
Attach the leather straps to the end pieces of the metal with your metal screws. These straps can be any width or thickness you desire, as long as they fit comfortably and secure the metal pieces to your arms and torso. There should be a minimum of two leather straps on the front of the body armour and two on the back. Attach your torso metal pieces to the straps, beginning at the bottom and working up. Overlap each layer of metal by about a quarter-inch. The effect should be one almost of scales on a lizard--one row overlaps the other.
Attach your shoulder pieces to the torso with the leather straps, and then the arm pieces to the shoulder blades, following the same pattern you had with the torso section. At each stage, try on the suit to make certain of the fit.
Always consult a professional if you are not completely comfortable with metalworking. Remember that Roman armour was meant to be applied with help, as the complicated straps make it impossible to do alone.
Always use caution when dealing with fire and power tools. Safety equipment, such as goggles and gloves, are a must.