Double garage roof trusses

Hi really not sure on all the terminology but here goes. Moved into a new build with a detached double garage of approx 5.5mtrs square. It has a tiled apex roof made of pre-made trusses. I thought it would be a good idea to board out the roof space to make some usable loft space, however I have measured the wood that makes up the joists etc at approx 38mm x 75mm with a joist spacing of approx 600mm and as mentioned a span of 5.5mts approx. There are not supporting walls etc in the garage it is one large open space of 5.5 x5.5mtrs. Surely the joists should be far more substantial for that kind of span? Can anyone please advise and what can I do if the builder has not followed regulations during construction? Thanks in advance.
P.S the truss design I think is a Fink W from what I can gather looking at google images

Fear not, they are prefabricated trusses and designed down to a minimum, they are absolutely fine. The joists as you call them are not actually joists, they are ties which are tying the bottom of the rafters together.

Stick some chipboard down on top and store light stuff up there only by all means but they are not designed to work as a floor to use as a usable space.

Thanks for that Freddystwin. That reassures me. Regarding the chipboard though, I see it is 15kilo per pack of three and I could need around 18 packs to completely board the space out. That would equal 270 Kg of chipboard up there let alone what gets stored (which would be small stuff). Is there a lighter option or do you still think it okay to deck out with chipboard? Thanks again

The roof will experience a lot more load than 270 kg spread over it, just on a windy day.

Crack on. Just don't be silly with the storage.

Yes and imagine a couple of fat builders walking around your trusses when they were installing it, the trusses didn't fail did they!

Not that I'm saying all builders are fat of course.

noseall

Down to 12st 4.

Not bad for a (shade under) 6' builder.