There are a lot of ways to answer this and a lot more questions to ask about your particular ramp... without knowing those first, here are some general rules to best control your ramps in the way you desire:
1. be aware of where your ramp starts and ends in the properties. just like a stair, it should go from one level to another. and you should always control it in that way... using the offsets if it does not go exactly to a level.
2. if you want the ramp to be continuous (and not to code) in the type properties, you will want to change the maximum incline length to some arbitrary number like 5,000. what that number does, is create the breaks and landings you get in your ramps if you leave it at 30' which is to ADA compliance. You can also change the slope if desired as well.
With that being said, one option is to put the base of your ramp at level 1 and the top at level 13. Based on whatever your slope is, Revit will calculate how long your ramp has to be... in this case it will be extremely long. Every time you click your mouse to create a segment of the ramp, it will create a landing between the next point you click. This scenario is fine if the ramp is mostly straight or zigzags slightly.
But if it eventually crosses over itself (which I imagine it would if it is 13 stories high) it would be better to create the ramp one or two levels at a time. I've done something similar in that way before myself, and using lots of reference planes is a big help also. So again, the important thing is to pay attention to the base and top constraints of each of your individual ramps.
Like most things in Revit, lots of good preplanning will make your life much easier. Good luck!
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