Well being on a second floor patio I would say stay away from charcoal grills. The chance of coals dropping out of a grill onto your wooden patio is very high, that and unless you can wash out your Charcoal grill on a regular basis with water, it won't last as long as a gas grill. So that leaves gas or electric. You now need to determine what you tend to grill the most. If you like grilling steaks then you want propane, and one with a high BTU output. Electric grills don't have that ability, they generally only get up to about 300 maybe 400 degree's on electric, which is fine for chicken and fish, but not ideal for steaks. Electric are nice for convenience but to me impart an off taste to foods cooked on them. So I suggest a gas grill, easy in use, more variety on temp range, rotisserie, smoking, and side burners, but invest in a high quality one. I personally like the Weber's (I owned a Weber Genesis for the past 8 years, and only recently replaced burners.) Outside of that look for cast iron grates, and if possible cast iron burners, infrared or wave plates that emulate infrared cooking for higher temps for steaks, and being on second floor patio look for one that comes with drip catch pan underneath, and invest in grill pad for the floor. Good hunting..