leveling new solid floor with old wooden floor

[browfish]

I am building an extension and have cast the concrete floor slab.
My question is, when i knock the walls down to open up the exisitng property, how do i level the new floor with the old suspended wooden floor the other side of the wall?

should i knock the walls down to the level of that slab, add shuttering and screen up to this? Or should i knock the walls down to just below the finished floor height so that the base of the wall acts as part of the floor?
Or some other way?

thanks