We have been using floors instead of ramps a lot for irregularly shaped submerged parking/roads. We like to build as much of it as we can with ramps first, because we find the tool helps a little figure things out. Then once we have the ramps worked out, we create floors on top of them and either add slope arrows if they are straight or add points if they are curved/irregular. MLANAO, to add points, create a floor with the plan profile you want. After you finish it, select it and you'll see up on the ribbon next to "Edit Boundary" command the "Modify Sub Elements" command. You'll then see green grips and dashed edges. You can use the "Add Points," "Add Split Line," and "Pick Supports" to start shaping the floor in section/elevation. It's just a workaround, but it's the best we've found until they finally get around to improving the ramps.
floor-ramp.jpg
You can see the walls that attach to the bottom of the floor.