Wheelbuilding / Wheel Building / Wheel build help

How can you tell which direction a rim is drilled? The one I'm thinking of is supposedly left-handed, but all the holes look to be dead centre to me, which is unhelpful.
I'm not quite sure what you mean here. Most low profile rims have a zero drilling offset angle. Deep section wheels often have an drilling offset angle alternating in direction, as it assumes you will be alternating which side of the hub you are lacing to. This easy to see from the outside of the rim.

I cant see how a rim could be drilled left-handed, and if it was ould'nt you just turn it around?. I havent had my morning coffee yet though.