Another option is to use a military grade 25W amps with a 24dBi directional antennas and stay inside the building. With an EIRP of 6250 Watts, it is a bit over the FCC Maximum. :)
I say this all in jest, but you may be surprised how many systems I have seen that try to penetrate concrete with 80W of power.
On a serious note, you could use a passive repeater on another building if the reflection doesn't work.