Raise a section or lower the other section of a floor

In my kitchen three quarters of the room is on suspended timber boards and the final quarter is tiled concrete. The concrete is about six inches lower than the timber flooring with three vents on the step to allow for ventilation. I need the whole floor to be on one level to allow for a kitchen refit. My question is whether it's easier and cheaper to somehow raise the level of the concrete section and subsequently raise the location of the french doors to outside or lower the level of the suspended timber floor to match the concrete. I assume raising the concrete is the simpler option but the ventilation must be retain for under the timber somehow. Once the floor is level a new tiled laminate floor will go over the whole thing.