I get you there's two different roof lines running with each other ,the problem is you can't reach the vent because the lower roof is in your way , what you need is a ladder hook witch goes on a different ladder ,witch you carry up there and hook the peak , of the first roof , then climb on that and get your work done on the higher gable , national ladder is we're you by ladder not home depot if you wish to live , ladder leaver legs OMG your going to die , if your ladders not level then get a claw hammer and dig in the dirt till it is , ladder can't kick out if it's dug in , if it's not straight up and it shifts your going for a ladder ride , not fun been there , watch a guy brake both arms when his ladder kicked out boy did he scream , you get up there put screws or nails on each side of your ladder if it a little squirrelly , there's other ways too , if you can't just walk up there , get like a 42 footer ladder and just run it up the roof and use your truck tire to hold the bottom of your ladder so it doesn't kick out , truck tire works on drive ways also . I was a rough frame carpenter for 20 plus years and we built big custom homes with big roofs , it got scary sometimes but we learned from it ,