HMDA requires reporting of improvements to the dwelling or the real property. Personal property is not reported. The shed does not need to be on a permanent foundation to be real property. If this was a dog house, I would call it personal property. The shed I have pictured in my head is not something that would move with the owner if they sold the home. However, if it was, that could be personal property and would not be reportable. Let's assume it's real property for the remainder of my response.
A shed is improvements to the real property. Thus, the loan is HMDA reportable, IF the loan is:
1) secured by a dwelling, or
2) classified by the bank as a home improvement loan.