I have built several sheds and if your patient free stuff can be found to do a diy build. Cheapish wooden sheds at DIY shops are poor in quality. I have put a metal shed up (it was bought from Argos ) its far better than wood but putting it together was a pain in the rump, fiddly and it took a few days to complete but zero maintenance and it looks like new 5 years on, still got my bloodstains on the inside off numerous knuckle cuts.