I often just edit a Revit floor to attach the walls below to the floor. This joins the geometry automatically. When some new walls are added, I just edit the footprint of the floor, change nothing, then exercise the option to attach the walls after edit. The option appears automatically, as shown below.

However, recently, in a structural course I presented, an exercise depended on offsetting some existing lines off the floor when walls were attached. I found that tabbing on a wall to select all the connected lines fail. I was at a loss of what to do, and then I had an inspiration. Detach the walls from the floor. This worked. The offset of the floor elements then behaved as usual. Strangely this is not always the case, but in that specific instance, it was a problem.

After the operation is done, one can then reattach the walls to the floor. Unfortunately, then must detach all the floors, typically on the outside.
What this teaches one is that Revit can behave in unconventional ways when operations are made on elements one can expect other operations to be impacted. Often one finds that one needs to experiment with the platform to figure out how it behaves in certain circumstances. Stick to well-established practices if possible. Keep it simple if you can. Introduce complexity towards the end. These actions might just make your modeling career easier to manage.
If you need help adopting Revit or BIM in your practice, please contact micrographics so we may be of assistance.