Hey,
I build a lot of things by myself for my hamster, here a few examples:
A little climbing-thing. I used "Ponal"-glue, because its not toxically and qualified for children too, branches and dowel pins. In Germany we often build things with these dowel pins XD
Then i made something from styrofoam and tile adhesive what looks like a rock.
(click on the image to enlarge)
A tunnel from wet toiletpaper. I let it dry on the radiator.
(click on the image to enlarge)
A house with two chambers und a platform, in germany we call it "race course", because the hamster can run 1 meter without a barricade XD
(click on the image to enlarge)
Greets