Tin roofs tend to get condensation on the underside which will drip all over your stuff.
You might want to consider fibre cement sheets which look look exactly like the asbestos ones you have now but won't cause condensation.
I did a shed in second hand tin sheets, but of course they already have holes in from the old fixings. I've spent hours putting nuts and bolts through the holes to stop the leaks, but it's still leaks....I rue the day, should have just shelled out for new.