Hate to disagree with some of the other posters, but I'd stay away from 110 units, they just don't have the power to weld THICK material.
If all you're going to do is sheet metal work, they are the IDEAL welder, they will weld sheet metal better than a 220 welder primarily because you can really slow down the wire speed and put very little heat into the metal. For example, Miller 110 and 220 units both have the same initial voltage, but the 220 units slowest wire speed is 60 inches per minute, while the 110 unit will go as low as 15 inches of wire per minute. Thus, both machines claim to be able to weld 22-24 gauge sheet metal, but since you can really slow down the wire speed you'll have a lot more success with the 110, as you won't blow as many holes in the material.
If you plan to install roll bars or weld in subframe connectors, I think you'd be a lot happier with a 220 unit. One way to mitigate the higher wire speed in a 220 unit is to us .023 wire instead of .030. .030 wire is the do-all wire, but in a 220 unit this thicker wire will put a lot more heat into the material.
Finally, if you can take a class at your local community college, it will be time well spent.
Regards,
Joe Dokes