And to answer your question, take a look at the platform sections in the Talking T Gauge Shop.....and you'll see I've put the platform structure on its own little platform to compensate for the built-in track bed.
On the platforms I've done for my Bridge layout, I still needed to build the platform up....but by the height of a sleeper. I'm using flexitrack.
The thing that I have done in the past is to try and get the ground level that platforms etc are being built on the same as the lower height of the sleepers, especially in other scales because it gives you more scope, also by building up the ground you can then use the slope on the track bed sides to simulate drainage channels by the track. The same height difference will apply to bridges and tunnel mouths or any over track structure
Mike based in deepest Surrey
Posting most of the time from a mobile phone please excuse typos