how to add colliders to several objects?

I have a building made of several objects and I need to add collision to it. what would be the best way to go about this, because I don’t want to have to add colliders to each object individually. If it helps, several of the objects are grouped. for example, a pillar has all the objects that make it up in on big group.

Put the collider on the grouping game object. A bounding box is the simplest way, but you could make a mesh collider that approximates your child objects.