What is the best way to support a roof over a porch when you are replacing the deck of the porch?

it is best to support the joists from underneath with 4x4s. This is going to require two peope to set up. one holds a 4x4 against the bottom of the joists and the other person cuts another 4x4 to go underneath on each end. this will support from underneath and you can access the roof without compromising the structure, or worse, your safety.