A while ago, I decided that I wanted to start doing some more serious metal-working and start in the art of manliness: blacksmithing. My only trouble was that I couldnt find many easy ways of building one, so I began planning and building for myself! Hope this helps anyone with the same predicament.
Step 1: Your materials
58 cement or fire bricks, preferably with the dimensions along the lines of 12"x5"x5"
Steel grating that will be as wide and long as your forge
Air supply/bellows (I used a shop-vac in this case)
Step 2: Laying your bricks
Next, you will want to flatten the ground you wish to use for your forge. You could even get some extra bricks and use them as a foundation.
Finally, based on your plan, start laying your bricks down. For my particular forge, I wanted it to be a pretty decent size, so I laid them so that there were 2 full brick lengths on each side.
Step 3: Incorporating your bellows
Once you have reached the 5th layer of bricks, slide a brick over far enough to fit the nozzle of your vacuum in. You may cut the protruding part of the brick off for aesthetics, however I did not.