Near the top of my build list is a forge, soon I hope. I have lots of plans for forges, and some ideas of my own. One plan that I have always found attractive was published by David J. Gingery Publishing back in the 90's. It was built and the manual written up by William T. Goodman and Robert W. Holmee. It has a very nice appearance but I would make some changes to the shape and refractory of the firing chamber. The refractory in the plan is a little thin in my opinion and there are more efficient materials that can be used today.
It took me a while to find this book, I think I eventually found it on a torrent site. The scan is not great (I cleaned up the two pages below), but it is complete. So if you would like a proven plan for a nice and very convenient forge or just want some good ideas for building one, this should do it.
To download go to my Books - Free Downloads page. # 65 - 4 MB - pdf