Completion Strategy:

Meh, this level is boring, or at least I don't like it.
The Stone Golem has lots and lots of life, it'll take a lot of firepower to bring him down.
Your going to need to fire either 6 rockets at him, or 6 homing rockets before he dies.
The Homing Launcher is to the left of the building in the middle of the site, up some stairs and sitting on a ledge.
The rocket launcher can be found either in the 'underground' area (which you don't really want to go to) or under some stairs near the homing launcher, go there.
Just try grabbing them as fast as you can and shooting two secondary fires at him (but MAKE SURE THEY HIT!).
For a more detailed strat, read the platinum strategy.

- Neo

Platinum/Fast Time Strategy:

Ok, as mentioned in the completion strategy, you want the Homing Launcher AND the rocket launcher (See Above for locations).
Grab them both as quickly as you can, then when you find him, fire 6 homing missiles at him (2 secondary fires, make sure they hit!).
When he dies, switch to the Rocket Launcher, then find him again.
When you do, same deal applies, 6 rockets, which is 2 secondary fires.
Be careful though, you will have to be pretty close for them all to hit.
When he's died for the second time, go back and grab more homing launcher and rocket launcher ammo.
Repeat until you've taken down all his lives.
If you've done it fast enough (which isn't hard), you should get a platinum :)

- Neo