Hey @Anonymous
It depends on the type of walls you are drawing
If it is a structural wall; it is always drawn in the downward sense...ie: if your current level is Level 3 and you want to draw a structural wall 4 meters high
=> Revit will draw this wall from Level 2 up tol Level 3...therefore you see on your properties pallete: Base Constraint : Level 3 and the base offset is -4000.
- Once you draw it; you will not see it because it will be below the Level 3 slab.
If you find that confusing...
- Use Architectural walls
- once done select the walls you need to be structural and check the Structural checkbox in the properties palette.