I am a graphic designer with a full time job in digital marketing at a grocery chain. With that being said I have very limited knowledge of pricing artwork for freelance purposes and have been known to leave a lot of money on the table in the past.
Recently, I landed a project working with a Twitch streamer, illustrating for merchandise. Specifically, they wanted a "logo" (although they aren't fully branded) on the front of the shirt, and a large illustration on the back. Initially I agreed to work for an hourly rate, however, after a couple of days we ended up renegotiating to a % rate royalty agreement. I have been reading up on this subject matter and have a loose grasp on this legality, and it seems simple enough for one illustration.
In this instance however, I'm curious how I would go about writing a contract if this client wants to use illustrations for multiple pieces of merch (Shirts, Hoodies, Hats, Stickers, etc).
It's worth mentioning that this was only talked about briefly, and I'm not sure if they would want the same illustration placed on multiple different types of merch, or if they want different illustrations per piece of merch.
Is there a way that I can include all of this in one contract if only the shirt is being negotiated? Would I have to draft new contracts per article of apparel as they come up?