Determine how big the table top needs to be. When you know this you will know where you need to cut the glass. Write the measurements down and then transfer them to a large piece of glass.
Place the large piece of glass on a big flat surface. If you can set the glass on a large counter top or table, that would be the best solution.
Score the glass with a diamond point glass cutter. Place a large steel cork-backed ruler along the line where you are going to cut the glass. Hold the ruler firmly and use it as a guide to score the glass with the diamond point glass cutter.
Position the large sheet of glass so the score line is lined up with the edge of the counter top or table. The larger area of glass should be on the table while you hold the other part of the glass with both hands. If the glass sheet is very large you may need to have a friend help you hold the glass in place.
Lift the glass sheet slightly and then lower it to break the sheet in half along the score line.
Smooth the cut edge of the glass by grinding it on a grindstone. You can also rub the edge with a whetstone and a small amount of water.