There are many ways to go about making a ghost trap. Essentially the trap is two boxes that slot within each other, so many opt to scratch build. A number of materials can be used to create your trap, aluminium, MDF and foam board are regularly used to create very clean looking replicas.
An outstanding example of a aluminium Ghostbusters 1 hero trap.
This trap is made from foamcore board and styrene. These are excellent materials if you are planning on making your trap lightweight. Perfect for a belt hanger.
An MDF trap. Though much heavier than foamcore and styrene, it’s far stronger. Moving through crowds at a convention or event, it’s important that your trap be built as strong as you can make it.
Alternatively, there are a number of people in the Ghostbusters community who offer trap kits. The majority of kits are made from resin though there are some sellers who offer aluminium trap kits, though these are pricey.
A Ben of Kent trap kit available from https://www.benofkentprops.com
Another example of a trap kit. You can find many sellers offering kits on www.gbfans.com within the For Sale section.