How to sketch a deflector that is angled to a curved surface

[rodMW2RH]

I need to sketch a deflector that mates at an angle to a curved surface. In the below image you can see the deflector at the top rear of the engineer's cab. A section of a cone does not work because the joint between the deflector and the cab roof must be a straight line across the cab roof. I'm new to Fusion 360 and haven't been able to do this. I need just the sketch so I can have the part laser cut.

[davebYYPCU]

For laser cutting you need flat pattern converted to dxf.

For flat pattern you need sheet metal area tools.

Flange

Are you talking about part B?

or the others that are a maybe?

[rodMW2RH]

Thanks. I'm talking about part B.