Approximately 10'*10'. That's the size I would pick in preference anyway. By happy coincidence I get Silnylon off the roll in a 1.5m width. 6m of that makes me a roof roughly 10'*10'.
Rigging wise usually some variation of the classic A shape. I've usually got enough gear that I'm not dependent on a fire for warmth so I only use the lean-to shape for very casual pitches, sunshade type of thing, or as a quick umbrella in mild rain when pausing for coffee and a few pipes. I find the classic A to be the most watertight in foul conditions and the one that traps the most dead air. I say variation of the classic A because I do like to recover headroom in a similar sort of way to the advantages of a dome tent. By having additional lines set a little lower the apex I can make the make the slopes more obtuse at the top. That reduces wind flap and gives me more usable volume.