I like the idea of more Offense but too many wasted points. Just 9 offense means 4 pts in Attack Speed which is totally worthless.
My favourite way of playing AD Malz is starting with magic items (That E...) then progressing to AD later on, but definitely getting at least 9 points in offense. When I hit them, I try make it so I can E W R and then my minion comes out. That ult holds them in place to let W/the minions do their work which gets me a decent amount of magic damage and a huge amount of minion damage respectively. It also sets you up later on when you decide that since they're building too much armour, it's time to grab an Archangels to go with that Manamune and Hybrid it up.
Because you can and it's funny. He's actually the best champion in the game (in my opinion) in terms of being able to switch between AD and AP on the fly based on the team composition. AD is still fun though, Frozen Heart, defensive boots, everything else is pretty normal. Even if you don't grab the Archangels, your spells are fantastic without AP so having the 10%MPen won't be wasted.