The Faraday cage should be made as an enclosed conductive-wall room. You do not define the size you need for the instruments inside. Do you assume a person inside?
The Faraday cage can be made of one-layer perforated conductive walls. The hole size for 2.45 GHz can be made < 1 cm as a cut-off waveguide. The door should be provided with tight conducting strips to ensure a good uninterrupted contact along the sides. All AC power and signal connectors should be provided with blocking/filtering devices that should suppress the 2.45 GHz signal by > 90 dB.
Designing such cage is not an easy project. It is better to contact your local government or university operating an anechoic chamber for EMS testing, and rent it for the time needed for your tests.
There are companies , e.g. ETS Lindgren and others, offering commercial Faraday cages.