I'd get rid of those mushroom slotted bolts too ....they're what people use when they only have their local hardware shop for fasteners..... they'll have the tensile strength of cheese and shouldn't be used anywhere structural ..... replace with hex head of a decent strength if possible .
Looking forward to your progress ..... makes me appreciate having big sheds after all the years of working out in the elements ....far too old to be doing stuff like digging down through the snow so I could wriggle under cars on my drive !
K
