Basically, as long as you're not propping a ramp inside a trigger it will work off any system floor with no fuss as long as (reference Wraiths' post above) the angle is not too acute and also bear in mind the more acute then generally the slower the avatar moves.
If you were to make a flat platform and from this an angled ramp you could throw the angle in any old how on the lower flat platform and it would just work if it roughly crosses through the flat section end. The trouble is always the 2nd connection ie top of the angled piece. The red collider lines must meet that of the angle and the top flat ramp or have a very slight gap. To do this you need to see both sets of colliders at the same time. Select the properties of the one you don't want to move, first. In this case the ramp, then hover the mouse cursor over the top flat prop, sliding the cursor to the right of "Properties" on the 2nd prop should leave both red colliders showing and leaving you able to move the second prop (the flat top) toward the angled ramp. The two red colliders must be the top most collide lines of each prop and no doubt someone will post an image soon. I am moving mine from PB at the moment.
Once you have this set of 3 props you would add the steps themselves and make this scaffold as I call it invisible. The bottom flat prop may be the system floor instead. Many use Court Floor for the stair props (as they can be textured) but due to the thickness of the prop it occasionally fails but is generally to be relied on. I myself use Flat Plane, as I was taught by the great Peter. One other area that causes or can cause problems is some ramps will not work off a full size floor and need a few size 1.00 x 1.00 pieces at the top/bottom before adding the rest of the floor. I personally would, unless a system generated floor, make all individual props from the same material. ie Floor, ceiling and ramps would be Flat Plane with a textured
non collidable floor over the top of the Flat Plane and the Flat Plane made invisible in the State Tab once all testing is complete. Mix props and you are asking for trouble.
Give me a shout any time in world and I will freely take you around my tutorial course I made. It is similar to Peters and I freely give away the info but not on spiral stairs. However Peter has now made this info freely available too so it should no longer be a problem hopefully. Stairs are possible in all properties.... I went to a place where they had not been fixed in 2 years. Many experts tried and as it was in a corner butting up to multiple walls I think they found great problem. Some 20 minutes later I was out of there and the stairs worked perfectly for the first time in 2 years, thanks to Peter, not me as without the knowledge he passed on I would have very little to help people with.
NOTE: My nick and image are from a company. That company allows people to use them both as long as they get permission and a licence. I have that and a certificate to prove it.
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