The dies I have used for these cards are called stacked tiles, so stacking them was kind of obvious, right. Using monochromatic colours or lots of different ones will give you cool designs either way! Stack just circles or just squares or mix and match, there are lots of options to combine.
(All supplies are linked to different stores at the end of this post in the thumbnails. The different stores are also linked behind the product name. Among them are affiliate links that may be used at no cost to you.)