I wonder if you could please advise:

We have just had our thatch entertainment area removed and have had a patio ceiling structure installed.  This incorporates a fascia and gutter ceiling.The frame is galvanized and is cladded with Chromadek.  The ceiling type is Isoboard.

Do we require plans for this structure?

Les advises:

If you were only replacing the roof sheets without changing the structure, then you would not need a plan. That would be considered to be a maintenance issue. The fact that you are changing the nature of the structure itself means that you will need to submit a plan. You will likely need an engineer to certify the design of the roof structure as well.

I hope that this helps.