That is an interesting cage primobellator.
What are the dimensions?
How easy is it to clean?
What are you using for bedding?
You might want to add a house, hammocks, tubes (4 inch diameter drainage pipe cut to 18 inch lengths is great in the cage and in the play area with T connectors), a solid 12 inch diameter wheel, boxes, a water dish that can not be upset (can't tell if you have one), a few corner litter boxes on the various levels (for litter and also safe places to sit, hide food, build nests etc), etc ....... there are some interesting ideas in some of the pictures posted of peoples cages in various threads on this forum.
I recently read a warning that rats have gotten part of their bodies stuck in toilet paper rolls and suffocated .... so they suggest that if you use toilet paper (or paper towel) rolls, that you cut them lengthwise.
Please know that not only is it normal for rats to chew wood, but they will pee all over the shelves and ramps in your cage and they will soon stink.
- If you do decide to replace the shelves at some point, you might consider using sturdy baking cooling racks cable (zip) tied on and covered with dollar store dish drain trays cut to fit and cable tied on - I have found this to work well, although they will hew the plastic so the dish drain trays will need to be replaced once in awhile.
...... and you can purchase the ladders that come with the critter nation cage separately or get some powder coated ramps made by martinscages.com
........ an industrious rat will be able to quickly chew his way out of the wooden cage top so you may want to replace it with a removable wire lid. If your bin came with a lid, you might be able to use it if you cut out the center of the lid and cover the hole(s) with attached wire or baking cooling racks
.......... It may just be the pictures but it looks like a rat could get out where your two cages meet.
Hope you post some pictures of your rattie boy(s) enjoying their nice cage