Hi Nigel
If you can mail me a pencil sketch of a side to show elevation and also a plan I can advise and provide a detailed drawing I can then assist with more answers.
In any cases the maximum clear span between the beams (supporting ends) for a C24 47 x 150 joist is 3.24m assuming 400mm centres. You can increase this to a maximum span of 3.47m if you used 300mm centres on your joists. Remember that your joists need to sail pass the supporting beam by 70mm. This construction will provide a 1.5kN live load for your decking.
Do consider that commercial decking installations do require a 4kN live load and also you are required to provide an 1100mm balustrade should the elevation difference be more than 600mm.
I love good causes
Karl
Per Ardva Ad Astra