Sounds like I’d start by deciding on the angle. Personally I dislike drawing people, so I’d do a birdview panoramic to show wall’s massive features from above and a mass behind (no details), and a series of messy panels highlighting details of soldiers holding the door. Like a hand pushing, some feet blocking, some shouting face, some weapon being prepared with door as background, etc. And then another series in different color maybe for the attacking side../