Build on Ramps
This is more of a bunch of notes than a tutorial on how to build on ramps, but I finally figured it out.
Part 1: Footprint
You need to alter the structure's footprint. I'm going to assume you have a basic idea how to do this.
1. Data Editor >> Footprints >> Your footprint >> Layers >> Placement Check >> Uncheck "no build". If you want it so it won't put it in stupid places, simply check "ground - no spawn". This will make it so it can be built anywhere a siege tank will go.
2. Data Editor >> Footprints >> Your footprint >> Shape >> Placement Check >> Uncheck ""no build". If you want it so it won't put it in stupid places, simply check "ground - no spawn". This will make it so it can be built anywhere a siege tanks will go.
3. Apply the footprint to the unit (anywhere it would apply is where I put it, the big one is in the Units >> Footprint (Placement) part of the units tab of the data editor.
Part 2: Pathing
1. Layers >> Pathing >> Add pathing type "Ground" >> Add the ground-type pathing to the ramps and only the ramps.
This was the missing step. I don't know about all the footprint changes but it seems now those will only apply to places where there is custom pathing. So now I have used the same method to make it so I have a placement and pathing blocker doodad in the middle of space.