Simple, easy, quick, I need a solution fast but I’m too stupid to figure it out/too lazy to actually shape the floor. I need to make a floor for this vvv
you don’t need to make a new mesh for the floor, since you already have the geometry there for the floor why not just reuse it (actual solution below)
if you want a cleaner solution, you could just select the fuselage mesh and select the loop where you want the floor to be and then duplicate it and seperate it from the mesh
then you could fill it in with f and either use knife cut or use j to get a cleaner topology
also if you want it to be actually solid then just extrude it down
The approach I’d take is definitely not the most efficient, but does work.
I’d duplicate the bottom half of the plane (up to where i’d want my floor to be), scale it to be flat & merge / remove all unneeded faces to decrease the Tri count.
Or the other approach I’d take is identical to what @sam_0987654321best said, but it generally depends on how fast the faces / vertices are to select.