Hello 
I’m not very versed with granny squares and I’m now at the question of which hook to use:
I have yarn that is ok to use for a 3,5-4,5 hook originally the pattern calls for a 4mm Hook and I have every size imaginable from 0,2-15mm but of course the 4mm Hook went into the abyss…
Would you rather size half a mm up or down for a granny square? (I use a cotton synthetic blend yarn)
Thanks in advance and a very lovely day to everyone! 
I would go down. It will make your stick a little bit tighter. Going up will make it more loose. So with that information it is up to you!
Thanks that what I thought but wanted to make sure :3
You’re doing great! Always trust your instincts!
down
up will be harder to use
I’d go down, if it’s too loose the square gets winkly/wavy
down if you don’t want it loose and out of shape in my opinion
It depends on the drape that you want
If you want a tighter fabric drape then a smaller hook size
If you want a looser fabric drape then you need a larger hook size
To tighten up the holes in the corners try chain 2 instead of the more common chain 3 that most patterns use
Everybody here has pretty much covered everything, but I just wanted to add that you can block/steam either of these to get a more uniform or drapier look!
