We have forms that we've developed for use in-house, which have to be heavily modified for each situation.
I don't think you're going to like my answer, but there aren't a lot of organizations that even try to do a commercial lease or purchase agreement template. The reason is that the terms of each commercial deal are so different from others.
If you don't already have forms that you use on an ongoing basis, then the best thing to do is draft a Letter of Intent (LOI) and have the terms drafted into a lease by an attorney that does this work all the time (so that you're not paying them to learn how to do it).
The LOI can be fairly simple -- put the terms you have in mind in plain language and have both parties agree to these terms before taking it to the attorney. And be sure everyone understands that the terms are non-binding until a lease is fully ratified, and add that as a line in the LOI so there is no misunderstanding.
Feb 21, 2010