Another question!! Converting a shed into a chicken coop

Without seeing the shed it's hard to say exactly but for the pophole, if you have a jigsaw you could drill a hole and then use the jigsaw from that to cut out a rectangle shape large enough for them.  Just be sure you cut this out of the cladding and don't affect the actual frame of the shed.

If they're in a secure run this probably won't need a door but if you want a door on there then you need to decide whether to just add something with hinges or build something which slides, which would then be compatible with an automatic opener.

Other things with a shed - just check there aren't any nails sticking out anywhere.  Is there ventillation?  Is there any damp?

Not sure what more to suggest.. I've probably patronised you already!!