When you're using power tools on a ladder at home, the last thing you want to do is have one fall and hit someone below. Instead of creating a hazard by setting it on top, add a holster to the side of your ladder for safer storage.
Build.com shows you how you can add a simple holster made from some PVC pipe. Find some 4" pipe and drill a small hole through the side and through an upper part of your ladder, then attach with a bolt. Now when you climb up there you have your power tool within reach, and it's a lot less likely to fall.
Note that you should only do this to your ladder at home. Altering tools can lead to fines on a job site. If you can't alter your ladder, consider a ladder with a built-in hole that offers the same convenience.
How To Make a Tool Holster and Attach It to Your Ladder [YouTube via Build]