original post hasn't appeared on my newsserver yet, so I'll reply to the reply ...
I whipped out my old building code (NZ, 1981) and they reckon for floor joists that for
joist spacing 400mm (~16 inches) 450 mm(18 inches) 600mm (2') size 9x2 4.3m (~14') 4.1m (~13'8") 3.7m (~12'4")
10x2 4.8m 4.6m 4.15m 12x2 5.75m (~19') 5.5m 5.0mthis is for a 1.5kPa floor loading. If the joists cover two or more spans, you can add 10% to the span. Huh, I want anybody to come up with a truckload of 42' long 12x2. (actually, the table starts with 4x2 joists spanning 5' at 2' centres, so that note is not entirely irrelevant).
So you can see that going on these numbers, the shed you looked at was quite sturdily built.
-P.