@roleplayer123 If you can get your creative juices flowing I'm sure that there's some way to make a chicken wire 'lid' that you are able to clamp closed, though I've never seen it done.. SO you may just need to mess around with a few ideas and see which one works best for you AND is functional. I wouldn't do no top at all, that seems risky, even if your rat isn't usually a climber, one night he could decide there's something that smells interesting outside his cage and wants to explore c:
@Meta No, I don't think those videos include levels. I couldn't personally find any really helpful videos of levels. But what I did when I had mainly tubs was just cut about a 4 1/2 -inch hole in the lid of the bottom tub and fit one of those drain tubes in it so the rats could climb up them (I didn't buy 100ft of it, lol, I bought some already cut). You don't really need to secure the second level to the first level, though if your rats are constantly try to escape you can drill tiny holes along the bottom outside of the top bin and zip-tie it to the lower bin's lid if it has a lip. (obviously after drilling holes in that as well.) And yes, if you mean clear bins those work just fine, it's mainly what I used until I switched to a bigger size in plain white.
**Edit: Note that theres a flaw with ziptieing the top tub to the bottom lid- every time you want to clean the tubs you have to cut the zip ties so you can disenfiect properly, which, in the long run was a turn off for me cause that I big waste.