Godbound doesn't generally do expansive modelling of physics. That said, there are a few ways to handle this.
Make it a zone of danger. (p27 Godbound) if their enemy is a word bound foe with access to miracles.
Create a Wall or Zone of Danger
Miracles to create a wall of fire, seal a victim in a stone block, or
otherwise create a hazardous zone take one round to form. If victims
in range move out of the zone that round, they take no damage. Otherwise, damage is usually one point per level per round in the zone.
From p 145, see how much damage they take.
Use half the creature’s
hit dice for level-dependent effects of the gift, rounded up, up to a
maximum of 10 for gifts used by creatures of 20 hit dice or more
You could also use some sort of smite, as mentioned above, doing 1d6 damage per two levels, or a normal corona of fury, for 1d8 damage per two levels for everyone within 30 feet.
If you want to add some interesting effects, see p169 for a list of impairments. For example.
Stun. Victim must make an appropriate
saving throw to take any action on a
round
Perhaps PCs could be forced to make a hardiness save to move and attack?
In terms of how tough a typical wall should be there is no guidance from Godbound, but SWN, another system he designed, has an answer from p42.
Instapanel: In its compressed form, an instapanel is a two-kilo
cube of ceraplast fve centimeters on a side. When a Type A power
cell is inserted in the cube’s side, it immediately expands to an
opaque, waterproof ceraplast sheet 2 meters on each side and a
centimeter thick. Five minutes later the ceraplast hardens into a
tough, rigid shape, but until then it can be folded or bent by hand.
Instapanels can be bonded to one another with a metatool or a
postech toolkit. Breaking an instapanel requires inflicting at least
twelve points of damage on it
Or alternatively, from hard light, p29, a super tough alien wall.
The tower walls are as durable as
hull plating, and have Armor 10 against non-Gunnery weapons.
It takes 20 points of damage to knock a human-sized hole in a
wall.
Godbound uses a conversion system of one Godbound hitpoint or hitdice to one SWN or D&D hitdice, not hitpoint. So a, level 4 fighter might have 4HD in Godbound. As such, if we divide 12 by 4.5, the average of a 1d8 hit dice, that suggests in godbound an instapanel would have around 2-3 HD, while a very tough wall might have 4-5 HD and have immunity to non magical weapons like swords. Unless your walls are notably tougher than an advanced futuristic wall material, they will probably break upon being hit with a smash of divine energy as such, which may do 5-10 damage. This is simply a rough estimate but generally walls don't do well around heavy weaponry.
To summarize-
Use a zone of danger, a smite, or an impairing condition, or some combination of the above. Unless the walls are made of a very powerful and advanced material, beyond futuristic alien alloys, they will probably break.
