Anyone know much in terms of cost of them?

Looking at getting one built, thinking along the lines of 15-18' wide and 23' long

Need to have a base built aswell and want the sort with a apex roof??

Anyone know what sort of cost they are, I was thinking 4-5k all in including building?

Plus is there are certain size I need to stay within before I would need planning permission??

Cherrs

Matt