I would stick with the commercial models. You didn't mention your budget or how much space you have so here are a couple options. The
Beverage Air BM23-2 will handle up to two 1/4 kegs. The
Bev Air DD48 will handle two half kegs. True Mfg. also makes similar models.
The key to outdoor operation is to give the unit plenty of air circulation. If you wish to build it into the bar leave a vent in back or the sides & you might also consider putting it on wheels to make service easier. You will have to eventually clean whatever you decide upon.
Later,
THE ICEMAN