I have this DesignScript Loop While reference in my bookmarks that could help to get started:
http://dynamobim.org/forums/topic/how-to-run-a-loop-on-a-dynamo-graph/
And also this example of LoopWhile using a custom node as a function:
But it don’t know (yet) if this could work in your case 
Edit: here is another good example:
http://dynamobim.com/forums/topic/loopwhile-for-a-variable-x-need-output-for-a-variable-y/