A detolf on top of a kallax is a common one
But that isn't a stack. I've seen people use stacked vivariums.
https://www.reptiles.swelluk.com/rep...varium-stacks/
They need adapting to add more ventilation
How many hamsters do you have? For two or three, just having one cage under a table and one on top of a table, with a cage on top of the top cage, can work.
There is also this two level cage. Someone on here blocked the entrance between the two and used it as two 100cm stacked cages. It's cheaper on ebay from Germany I think.
Sky Rat 100
I think the Kallax units are not very deep for making into a cage - especially for a Syrian.
There is a diy cage I've seen using Lack tables - stacked on top of each other.