Don't be so attached!

When creating/modifying a horizontal element (floor, ceiling, roof, etc) and you are asked if you want the walls to attach to the bottom - click NO.

Why you ask?  If you try to edit the height of those walls later, they will not budge and you (plus more importantly the rest of your team) will not know why they will not change, which in turn will cause fits of rage.  If you do find that the walls were attached, simply select "Detach Top/Base" from the Wall Context Tab and DETACH ALL.

Don't get me wrong.  There are times when you may want a wall to attach to the underside of a horizontal object which in most cases would be a sloping roof.  But these attachments should be done on a wall by wall basis and not all at once.  If you want your walls to come to the underside of a flat horizontal element, then a better method is to set the walls Top Constraint to the level that hosts the horizontal element.  Then use Top Offset to get the wall where it needs to be.

Since we are denying Revit, might as well say NO to it's request to cut volumes out of any walls that the horizontal element may intersect - again this should be done on an individual basis.