Red Faction: Guerrilla - 'Demolitions Master' Guide #2
Decided to do another one of these guides for another tricky demolition master challenge. Its simple enough when you finally nail how to do it. This should help those of you having trouble.
Extra Tip:
Though I did get lucky and didnt really have to use the nano rifle, keep in mind you may have to destroy additional struts with it to get the "crown" to fall. You may also need to break some additional concrete with your hammer around the corners if the "crown" doesn't take care of it. Just use some of the rocks near the building to get high enough to destroy it (hope you have your jetpack by this point...).