What are some ways to simulate an explosion?
If you're looking for a fireball explosion, you could download a visual effect of an explosion that's already green screened for you, and just composite that on top of your footage. (That could also be "borrowed" from an existing film and each frame masked by hand. But you didn't hear it from me.)

The building and anything nearby will need to be lit up temporarily by the brightness of the explosion, especially since the front of the building will be in shadow (with the sun behind the building, as you described in the comments to your answer).  I would recommend doing that as a practical effect with actual lights covered by actual orange gels at the actual location.

To help sell the effect, there should also be a blast wave (wind) that blows trees, bushes, people's clothing &amp; hair, nearby litter, etc.  You might show that with insert shots. The camera could also shake for an instant (even in post production) to show that the impact of the explosion even affected the camera.

I'd also include some bits of debris landing near the camera or in the scene to underscore that the explosion is happening in the same environment as the camera (and possibly characters).

For the explosion noise, lots of sound libraries have explosions and destruction sounds you can layer together. I like using a clean, fiery "boom" along with breaking glass and splintering wood, followed by staccato showering debris.