According to schools metalwork adviser P. F. Lye, a rolled lip on sheet metal is called a wired edge because you form it over a piece of wire. Use any diameter wire, depending on the size of lip you want. Normal practice is to use wire of about 1/8th inch diameter. Begin the rolling fold at a distance from the edge of the metal to accommodate the wire, which should be wider than your metal sheet so you can with withdraw it after it has served its purpose.
Multiply the diameter of the wire by 2 1/2. Write this down as value A.
Scribe a line on your metal, parallel to the edge you want to roll, at a distance from the edge equal to value A. Scribe the line 5/16 inch away from the edge if using 1/8 inch diameter wire.
Insert the metal into folding bars, aligning the scribed line with the inside line of the bars. Clamp the folding bars in the vice. Strike the proud edge of the metal with a mallet to bend it over at a 90 degree angle.
Remove the metal from the folding bars and lay it on the bench. Insert the wire along the line of the 90 degree bend. Tap the edge of the metal over the wire to form a round lip. Atonopedia suggests a sweeping action with the mallet.
Remove the wire.