You can't really deduct the value of your time.
So this is more like advertising for you doing this as a goodwill. You would them deduct the costs incurred just like other expenses you incur when doing the actual paid work.
So you might have have some travel and supplies that you incurred that would be deducted for doing this free work.
This type of work creates goodwill, gets your name out there and leads to some new clients hopefully, so it is a cost of doing business versus an actual charitable donation.