Have you decided whether to roof the run near the pop door?
...or you could add a foyer......lol!
I did this because pop door faces prevailing winds...oh, and wicked winters.
Just happened to have those windows around...so viola!
Maybe build your frame work level, lowest point of framing at highest point of ground, and the HC will just go past the lowest horizontal framing into your apron?
You could attach some 'dummy' verticals below bottom horizontal where needed to attach HC before it hits the ground.
Hope that makes...