Depends on how slim you want it. For most trousers, I like about 7-7.5" leg openings, tapered through the entire leg. For my white 501s though, I asked for a 7" opening and had the tailor pin the legs the whole way up.
Basically, have a conversation with your tailor, try on the jeans and have him pin it up while you’re there. If you want something done a certain way, then you have to communicate it. They’re not mindreaders.
ADDING noahzagor said:
Tapering selvage denim will make the selvage on your cuff look wider. Not necessarily a bad thing, but a clear marker that they’ve been tapered. Just something to consider.
Good point. I think that’s just something you’re going to have to decide: Do I live with a wider selvedge line or a wider leg opening?