Attic flooring - RSJs etc.

I'm thinking of getting the attic floored. Detached bungalow. Hip roof. Cut roof construction.

The attic would be used for storage. No permanent stairs, just the the Stira ladder that is already there. I would be storing some fairly heavy items in the attic. I would need lighting and sockets but no windows.

If RSJs were installed from gable end to gable end (not sure if gable is the correct terminology when the roof is a hip?) the max span between block walls would be about 6 metres.

Now I'm a bit confused about what I should look for and difference/similarities between a floored attic and an attic conversion. I have seen websites from attic flooring contractors and there is no mention of RSJs and prices seemed too cheap. I have also asked a couple of attic conversion contractors who were mentioning much higher prices with specific mention of RSJs but they either didn't get back to me or told me that they weren't interested in the work when I enquired.

Has anyone got any tips on how I could approach this and what I'd need to consider?

Thanks