Wow - thank you all for the excellent tips! Have used boric acid in the house but never outside around the shed - will give it a try.
Wayne - Most of the cracks are sealed with spray foam except the upper loft area so I will definitely be getting up there, then to seal more. Both rooms are insulated and dry-walled and there is one window plus the a/c unit which is permanently fitted and sealed. They also could be coming into the sink drain so will get stoppers.
Eli - There is a lot of standing water in leaves and potting dishes some I can eliminate - I wouldn't have thought about that - so good.
And I have noticed several lizards in the studio half of the shed - they house themselves behind the wall prints - Must Eat More!!!! Looks like I need more foam sealing - those giant roaches can slip through anything. and will try the Hot Shot.
The fungus now seems to be the biggest battle in protecting my lenses, leather parts and above all, negatives!
Thanks for all your tips.