Garage door stepdown

Hi guys
just a further question about a garage that I have planned. The slab will need a ramp from the street which I plan to cast into the slab, the garage door will be recessed slightly with blueboard walls to give a depth to the building to make it look like masonry construction. What is the best way to form a sloping recess like this into the concrete? With formwork or once the concrete has started to go off? The frame will sit as shown in the picture, hopefully keeping the place more water resistant.

Thanks
Pulse

Form it with the trowel after you have poured the slab. Formwork wont give you the same finish on the ramp as you will have on the slab and it will probably have voids in it. Just mark the extremities of the door so you know where to start it. It's good if the slope starts just in front of where the door comes down so that you don't get any water sitting in front of the door.

Thanks SilentC, just the info I needed
Pulse