If it's for a dwarf hamster (is it?) I would go with the Maxi duna multy. If it's for a Syrian I would go with the Barney.
You don't need to do diy for platforms. Can you get things from Getzoo in Germany? They do some great platforms. Alternatively this is a fairly good option from Amazon. It's a bit high for a dwarf hamster so you'd need deeper substrate in the platform area and a stable route up to the platform - you could have the house next to it for example, as a step up, then a bendy bridge on top of the house.
Assuming it's a maxi duna for a dwarf (the barney already has a shelf). The Barney is very tall for a dwarf hamster if you aren't wanting to do any diy.
I'd recommend a labyrinth house as well - plenty of space for a large house and the hamster will feel more secure as it's dark inside.
Trixie Natural Living Shelter, 30 x 22 x 25 cm : Amazon.co.uk: Pet Supplies
Incidentally - where do you find the Barney cage available? It's not available in the Uk any more on Zooplus (or even on the German Zooplus site) - I assumed they were no longer in production but maybe they are only selling in certain countries?