Safety comes first
You might be tempted simply to roll your existing propane grill under a new pergola. This won’t look as nice as a built-in grill, though. What’s more, mobile gas grills have stricter fire-safety clearance requirements than those of their built-in cousins.
A grilling station constructed for a rolling grill would look extremely ungainly because manufacturer’s instructions commonly demand clearances between 24 in. and 36 in. “from any wall or surface.”
These clearances are important. Not long ago, I forgot to turn off our mobile grill’s burners. After dinner, my wife looked out to our patio and yelled, “The grill’s on fire!” As odd as these words sounded, it was a fact: Our grill was on fire. The hood had become so hot that its exterior paint was burning in places. Luckily, a quick spray with the hose doused the flames.
The manufacturers’ installation instructions for both mobile and built-in grills state that you should not locate a grill under any “unprotected” combustible roof or eave. They mean exposed wood rafters, wood soffit boards, plywood decking, and so forth. If you’re going to use wood for a roof or a pergola, then it should be covered with a noncombustible material such as stucco or fiber-cement panels and/or trim boards.
If you really want to have exposed wood on your roof, despite manufacturers’ warnings, use good sense and allow extra clearance above the grill. I also recommend that you use stouter beams and rafters than normal. Additionally, be sure to check your local building codes for any restrictions regarding outdoor barbecues.