It all depends how much you want to spend,you wont beat the prices of store bought sheds ,so I presume you know that, so presume you want a pukka one,try having a look at Larry Haun on U Tube for construction methods,Designs would be on there too,or google shed images,go for a pitched roof they alway's look better than flat roofs, there is agood book for inspiration called Handmade houses,A guide to the woodbutchers art,let us know what you turn up