How many percent can ask for a game or film sound design ? Alternatively, an hourly rate or sound/piece. What do you think?
I sincerely doubt there is any standard for this, for film anyway, as every film requires individual consideration. Things to consider:
the script, whats the content? (a drama with 3 actors is obviously handled differently to an action movie)
the total budget vs the expectation
when does picture lock occur?
how is production sound? ie what % ADR is likely?
what are the deliveries required?
Putting together a budget for sound design for a film means justifying every hour of the entire teams work. How many weeks for dialogue editor, ADR, sound effects editor, foley team, foley editor, predubs, final mix, delieveries etc...
My suggestion would be to start with a fixed price. Get a feel for how you pace yourself as a sound designer. The speed of your work could vary depending on the quality of the production and what is asked of you. If you also have to clean up and edit audio in addition to creating the sound design, then that's going to affect the pace of your work.
I wonder if there's a resource that shows a standard breakdown of budget. I had this conversation earlier this year. In the end, I imagined a setup where the post production budget took up 20-25% of the total budget and out of that 20-25%, sound design wound up with 5 to 10%.