How to install a screen door in front of my front door so tha the doorknob isn't in the way?

the easiest way is to reverse the swing... that is to say, if standing outside and the door knob is on the left you make the screen door knob on the right. the problem is now the purists don't like the having to open the screen fully before you can open the door. The best approach is as you suggested build out the frame or casing to mount the screen 3" out and have the door knob and screen latch on top of one another but not interfering