I was asked to make a cake with dripping icing of gold, what is the best method to use over butter cream?

I will be doing the same in a few weeks :)  I plan on doing a ganache drip, some shade of yellow.  I have a squeeze bottle I put it in and then I can control the drips.  I start on the outside, doing the drips first and then I fill in the top.  After that dries, I will hand paint the drip gold, using an edible dust (and vodka).

I've never painted the drips before - but I do the same as above: a squeeze bottle filled with the ganache, same process mentioned. Make sure it's not super hot, but warm enough to flow nicely.  And chill the cake first so that the drips will seize up and not run straight down to the cake board and you have more control over the length of the drips (hold longer and squeeze a tad more for longer drips, less pressure for shorter ones....but maybe you already know this. Sorry if so;) 

I've never used ganache.  Do you have a recipe?

Most of the ganache recipes out there are quite similar, but this is the one I happen to use: 

8 oz semisweet chocolate (chips or broken bars)

1 cup heavy cream 

1 tbsp unsalted butter

*Heat the cream until hot, but not not boiling. Pour heated cream over chocolate chips in a bowl and let sit for 3-4 minutes so the cream will melt the chips. I also add the tbsp of butter in there at this point. Then after those few minutes, I stir until it's creamy. At this point its at a good consistency for piping drips, though don't do it while it's still hot, wait for it to cool a little and just be little warm. I always test it out on a plate or something to see if it's too hot (let it sit for a few minutes) or too cool and then I reheat it for a few seconds.