Hi thanks for your question. My name is ***** ***** I can help with this.
You can only gain "squatters rights" - or, more legally - acquire land by way of adverse possession, if you were not entitled to be on the land, or in the shed, concerned to start with. If you were, becasue the landlord gave you permission or keys to it, then you cannot claim "adverse possession".
If you were not there with permission, or stayed after permission was revoked, then if you have been there for more than 12 years, you may be able to claim advese possession.
Hope this answers your question.