Iam replacing an old shed I won't it to last for along time so I won't he best quality and thickness of wood materials ect it's in a shady part of the garden and will I thought have to be on a concrete base and rat and mice resent I also won't his fully damp treated including base and the wood highly treated I won't it also insulated as it will be used all year round with heating even when not used electricity and a log fire and the roof to be tiled and guttering so it lasts for ever with as little mantance as possible size roughly 15 by 14 feet single floor either under floor heating or night storage as it can be heated in the winter so it doesn't get damp but also a small log burner I won't the best wood I have know idear where to start iam disabled and won't his as a meditation room to help my disability please can you advise what's best I do have a rat problem which iam always having to sort and it is on a small slope to the ground would have to be levelled to many many thanks