I have been asked to re create this around the side of a cake, I can do the pattern work. But not great with piping royal icing so how would people recommend doing the straight line/border along the top?

Is there a picture? 

Best way to do icing is to hold the tip about an inch above the cake/cookie and let the icing fall, so to speak.  Easier to control that way.  And easier to keep it from being wobbly. 

Hope the helps.