How to 3D print a shopping cart
If you need a real shopping cart, please think about actual requirements.
Carts are sturdy devices, build on very consistent frame, because they are meant to carry heavy loads. The built must be focused on good jonts and durable wheels, otherwise forces from load or streatching would quickly damage the construction. Some parts of frame are normally under strain, and a direction of load forces is not always downwards, therefore frame has to be robust.
Cheap additive manufacturing technologies of standard printers are not suitable to produce objects of this size in one piece. If to follow this idea, one chellange would be to design pieces of the print, which could be connected or glued into a ready cart. 3d prints have tendency to snap along layers of print, therefore frame would need to be carefuly built from parts designed to be printed horizontally, rather than vertically. Construction of wheels carrying the cart with assumed load could be not possible, because load forces could mangle them very quickly.
Only the amount of material needed to print the whole thing could exceed cost of the cart. And the same would be about more expensive printing techniques, like printing of metal. The shopping cart is a good example of thing which is not worth printing (at least in 2021).
BTW: Shopping carts have some plastic parts, and printing these could be indeed possible. I suppose they are only protectors, not a part of cart construction frame.
I would advice to look to get a ready cart. Check locally for used, worn out or reconditioned shopping cart for your project.  Maybe even try to rent it somewhere. It would be much easier and quicker then trying to 3d print the cart, even if it is possible to do it within some reduced requirements.