I wrote something recently on how to create small tasks for estimating (http://keithba.net/estimate-like-a-boss http://keithba.net/estimate-like-a-boss), which

I wrote something recently on how to create small tasks for estimating (http://keithba.net/estimate-like-a-boss http://keithba.net/estimate-like-a-boss), which includes an example design doc and spreadsheet of the breakdown. You may find that example useful. Generally speaking, finding a way to communicate this will depend on the engineer. Someone very junior may require much more detail both in the technical design and the feature itself. Someone more senior needs less of that.