Wiring a shed
You should not use a temporary wireing method, like an extension cord for perminant wireing to the shed.
What you can do is to wire to a small transfer switch located at the shed. The transfer switch would have one feed from your panel and one feed from an inlet located where you could plug your generator cord in. The load from the transfer switch could feed a small sub panel which would have the shed loads connected there.
An inlet is like a recepicle outlet, but instead of having holes for a cords prongs, it has the prongs. The female end of the generators cord plugs into it.