What is the best practice for building a new wall on top of concrete to create a bay window, should we pour a concrete curb or use sill flashing under the framing?

Hey there! So, my husband and I are tackling a home renovation project where we’re turning our garage into a bedroom and making the garage door into a bay window. We’re planning on raising the floor by 11 inches and keeping the existing garage door header. The bay window will go from the ground to the soffit and sit directly on the concrete, which slopes slightly away from the house on our front porch.

We’re a bit unsure about whether we should raise the framing onto a concrete curb or use sill flashing (break metal) to prevent water damage. Any advice on the best way to go about this? We’d really appreciate your expertise on this matter!