Kind of spontaneously I made yesterday a lego-rug-bag. I have seen several examples of those on pinterest and thought that might be interesting for my kids. They don't like to tip over their lego-box as it takes them too much time to tidy up later. But it is much easier to find specific pieces, when the lego is spread out a bit.
As I didn't planned to do it yesterday, our rug turned out quite simple. It is cut out of a strong white fabric (I know that is not a very practical color). The diameter is about 1,40m. It is edged by a bias tape that holds about 20 loops where we put a strong cord through to pull it together.
First tests are showing it is working. Once you have all lego in the sac, you can easily fill the content back in the box.
I hope the kids will use it lots from now on...