What are my options to utilising space in my garage roof?

It’s about 6ft tall in the middle from the trussed rafters that run the whole span front to back, blockwork on one side and brick on the other.

I was thinking of hanging some 2 x 4 joists from joist hangers above the current trusses just in the centre part where I want to store. and putting some Moisture resistant MDF boarding on top.

Does this sound like a good idea or has anyone done anything different?

18mm chipboard flooring would be more suitable it is lighter and more rigid than MDF and is also available in MR. It is also tongue and groove so eliminates gaps.
If it is solely for storage I would fix directly to the existing timbers. Screws or nails.

Thanks, I did think of just laying boards over it but I don’t think it’s strong enough, the current beams are two beans end to end joined together.

Also I wanted to board out the bottom with plasterboard to give it more of a roomy feel so was thinking I shouldn’t put too much weight on it?