Code name “Baby”

[Abnorm]

^My new FAVORITE way to cut the roof is with a "Sandwich"..........I've done a square and round vent with this trick

I stack 2'x2' squares of foam insulation to a depth of the metal sabre (jig) saw blade......and back it with a single bottom crust of Plywood..........then JAM it UP in the desired interior location with a stout 2x4

NOW its a simple matter to drill/cut the opening from the roof side......the metal cutout never falls down......all the dirt and metal cuttings are contained in the foam.....the vibration of the saw is reduced especially if you really force the sandwich in place

YMMV