How high is the tower in question?
Is it set into a concrete base?.
I think that the NEC has something to say about the Lightning Protection for structures such as these.
What I would do is this:
Get 4 Ground Rods and drive them at at least 6' apart and bond them with bare copper of at least #4.
From there, take 4 wires from the tower to each Ground Rod.
This could be over-kill for your particular application , but it is better to be safe than sorry.
Also, any antenna that is on top of the tower should be fed via a Gaseous Surge Diverter, which should also be Grounded to the tower Grounding system.
The Impedance of the outside Grounding system needs to be a lot lower
than any Ground impedance on the inside of the building that that antenna feeds.
It needs to be that way to keep Lightning currents out of the building.
Oh and by the way Steve, it also has to be bonded to the Building Grounding system too, so that if there is a strike, the whole Grounding system is at the same potential during the current distribution of the energy.
Hope this helps.