What does architecture represent in the poem Beowulf?

The best way to ascertain what architecture represents in Beowulf is to closely analyze the poem's most important architectural structure: Heorot, Hrothgar's celebrated mead hall. 

Overall, Heorot is described as being an elegant structure built of wood and decorated with gold. It is an important gathering place for Hrothgar and his most trusted allies, and it primarily serves as a space for eating, drinking, celebrating, telling tales, and sleeping. More importantly, it is noted to...

The best way to ascertain what architecture represents in Beowulf is to closely analyze the poem's most important architectural structure: Heorot, Hrothgar's celebrated mead hall. 

Overall, Heorot is described as being an elegant structure built of wood and decorated with gold. It is an important gathering place for Hrothgar and his most trusted allies, and it primarily serves as a space for eating, drinking, celebrating, telling tales, and sleeping. More importantly, it is noted to be a place of light and joy, especially at night, and these latter qualities are ultimately the characteristics that anger Grendel. 

In short, we can see Heorot as a valuable community space in which members of a society are (supposedly) safe and secure from the dangerous wilderness. By extension, we can hypothesize that Heorot (and architecture in general in Beowulf) represents the safety and security of civilized society set apart from the chaos of the wild. As such, it's hardly surprising that Grendel's attacks are so subversive. They are not only acts of violence, but also attempts to undermine the order and stability of civilization itself.