Shed vents.

[Drawweight]

Any recommendations for vents to go through shed wall, Celotex and a plywood lining?

Just a cheap grille on the outside and a hole to the inside or is there a better way?

[sherman]

A plastic vent on the outside and a hole on the inside will work fine.
Just make sure there is fine mesh somewhere behind the outside vent to stop unwanted visitors from coming through.
Put the vents high up too.