what is best size of  a poultry shed of all the available designs ?

For tropical climates a 500 sft shed for 500 chicken , with all sides meshed and ht 12 ft and 3 ft overhang is a best , with 4 bulbs, 10 feeders and 10 drinkers. for other areas and climates pls send us ur personal requirements and conditions available

do poultry require sheds or housing or can they stay under trees and natural shades?

sheds, barns, or housing are required, or they tend to loose immunity and die in weather. 

Egg storage godown ?

its hould have good air, protection from sunlight, cool place , good away from pests, 

protection from snakes ?

nets along the meshes and ventilation areas to trap snakes.

protection from vultures or cats or dogs ?

a watchman or a watch dog is required to the protection

what is the barn size required for 500 hen ?

1000 sft place is required for them to move freely.

protection from fyying insects ?

fix a flying insect trapper with a net