Need Custom PolyLine Lisp

I need a command that will prompt the user to select objects and then trace around the outside of those objects with 4" or so of space. Though I know I could just do this manually, I typically do this on large areas with many angle changes which can become quite time consuming. I know this is a tall order but I remain optimistic. I honestly don't know where to start on this one but any input you guys have would be greatly appreciated. I attached an image of what the end result would look like to hopefully clarify.

This will get you most of the way there: Outline Objects

I was going to suggest:

(defun C:test ( / d SS )
(initget 1)
(setq d (getreal "\nSpecify offset distance :"))
(if (and d (setq SS (ssget)) (setq SS (LM:outline SS)))
	(progn
		(command "_.offset" d (ssname SS 0) "\\" "")
		(entdel (ssname SS 0))
	)
)
(princ)
)

This is definitely a place to start. Thanks guys! Any ideas on having it recognize unconnected objects as blocks and tracing around them as if they are connected?