I'm currently running a 7'x8' shed with 8' ceiling. It's fully insulated with an ac, dehuey, huey, heater, co2, exhaust fan and electric intake dampers-- allows the system to run sealed or open... depending on weather. All controlled with an arduino, some relays and sensors. The shed itself is the lung room, so to speak. Inside the shed I have a 3.3' x 3.3' tent with an ac infinity 6" fan (also controlled by the arduino). Next to the tent, on the other side of the environmental devices, is where I veg, clone, grow, etc. The tent fan is always running at 1 speed and ramps up if humidity is high and slows back down when it's low. I set it up so it's speed doesn't change depending on temps.
My lights turn on at 9:00PM and turn off at 9:00AM. My temps are always stable within 2 degrees F. I'm in SoCal, so we get some 100*F+ days, and this shed does fine. I use a 5000btu window banger.
Make sure to place the shed in as much shade as possible. Use white paint (I used ceramics added to the paint as well) to reflect radiant heat. I used OSB with the radiant shield on the ceiling as well.
To help with pests I cleared away as many plants as I can from around the shed and routinely spread neem/karanja on the path to the shed. My intake dampers have filters to prevent any bugs from getting sucked in.
I was thinking about adding one of these to the floor right by the door:
Clean Mat Replacement Pad - 24 x 36", Blue H-1570BLU - Uline