Choosing a Grill
Choose on burner count rather than BTU: three independently controlled burners give the hot and cool zones most cooking needs. Then grate material. Then, on a covered patio, clearance - a roof overhead changes where a grill can safely stand.
Burners before BTU
Three independently controlled burners let you sear over one and finish beside it, which is how anything thicker than a burger is cooked. That capability comes from zones, not from output, which is why burner count is the first number to compare. The full argument is in what BTU actually tells you.
Then the grates
Cast iron holds heat when cold food lands on it; thin steel loses it. Porcelain-enamelled cast iron keeps that behaviour and cleans more easily. This affects the cooking more than a ten thousand BTU difference does.
Then, under a roof, the clearance
A grill under a structure is a different proposition from one in the open. Manufacturers specify minimum clearances above and around, and a louvered roof closed flat is a ceiling for that purpose. This is worth checking in the instructions for both the grill and the structure, and it is not something a website can answer for a particular patio.
Clearance requirements come from the manufacturer's own instructions and from local rules. Nothing here replaces either.
The two here
The three-burner with a side stove is the everyday configuration. The five-burner combination adds a griddle and a pizza oven, and is the one to compare against buying three appliances. They are put head to head in three burners or five.
Questions
How many burners does a grill need?
Three independently controlled burners cover ordinary cooking, because they give a hot zone and a cool zone.
Can a gas grill be used under a pergola?
Clearances are specified by the manufacturer and vary. Check the instructions for both the grill and the structure.
Are cast iron grates worth it?
They hold heat when cold food lands, which affects cooking more than a modest difference in BTU.