Have 2 DSs aged 11 and 8 and their rooms are a disaster zone. There always seems to be so much STUFF lying around which means that when our cleaner comes she can't/won't do more than a quick hoover of the bits of carpet which are visible.
They're both into Lego, and like to keep the models they've made on display for ages (or in DS2's case... FOREVER) It's a dusting nightmare.
I sort of feel DH and I are a bit to blame as we've never got them into a good routine of tidying up every day etc. It tends to end up a big blitzes with tears ever few months 
Can you explain how you keep kids rooms tidy-ish please?
What rules/ routines/ responsibilies...?
They keep asking to have more friends for sleepovers, but I point out that they can't even see the floor, let alone put a spare mattress down!