Building a pen on a hillside?

[little buddy]

I like where I have my coop for my two new Bantams but building a run is going to be a challenge because of the sloped terrain. Any tips on how to deal with this would be appreciated.

 

[HighStreetCoop]

The main issue will be runoff and water. If you can trench, build a drain, deflect the runoff, you should be solid. If you run a few searches, you'll find people who've dealt with this.