Our first study was done on our own.
Our second study was done by a professional but they used the cash basis vs component basis and we utilized some of their figures to create another study.
To learn more about Reserve Studies along with info on how to complete one yourself see the following thread on this forum titled Reserve Studies/Funds 101:
http://www.hoatalk.com/Forum/tabid/55/forumid/1/postid/103517/view/topic/Default.aspx Note, some of the links on that thread no longer work but, if they were simply changed, then the links were updated later on in the thread.
Depending on what common components you have, a self study may be all you need. However, if you have stormwater detention ponds, are in a condominium complex or own a pool, you may want a professional study done where engineers actually inspect those components.
Hope this helps,
Tim