I would sue him in small claims court for the $5,000 in invoices. Let him raise and prove that clients have not paid him yet. That will take a huge amount of time, effort, and inconvenience to those customers and he will likely just agree to settle with you. You definitely need a new attorney to draft up your contracts. You never want a contract to be conditioned on something that you have ABSOLUTELY no control over - whether a client pay the architect.
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Mr. Leroi is correct. Sue in small claims. A pay-if-paid clause is strictly construed (meaning the courts do not like these).
Most importantly, doing work involving thousands of dollars of value should be well written and drafted by someone who is looking out for your interest, namely your attorney. A good contract is worth the price paid many times over as opposed to having no clue about what you are doing or relying on whatever they put in front of you to sign. Speak with an attorney to get the best advice on how to structure your complaint. Good luck.
This answer is for informational purposes only and is not legal advice regarding your question and does not establish an attorney-client relationship.
I agree with each of my learned colleagues -- call one of them for the help you need in putting together your case!!
In no way am I offering you legal advice, and in no way has my comment created an attorney-client relationship. You are not to rely upon my note above in any way, but insted need to sit down with counsel and share all relevant facts before receiving fully-informed legal advice. If you want to be completely sure of your rights, you must sit down with an experienced criminal defense attorney to be fully aware of your rights.