Advice on building mezzanine

We are about to start moving into a small (1000 sqft) warehouse/workshop and needing to figure out the best way to build a full second floor mezzanine for the place that will also be level up to the top of an existing 9ft tall office room and a bathroom.

The two options that I am looking into are either using pallet rack shelving as the base underneath to support everything, or to possibly bring in a couple of 20ft shipping containers and try to build the second floor on top of them, or maybe even a combination of both for the front half and the back half of the area.

If using the pallet rack shelving, by building multiple separate free-standing shelves placed front to back, what would be the best way or best material to use to connect them all together with some kind of cross member support laid on top, to also act as floor joists for the second level, and that would be able to go across all of the beams perpendicularly?

From looking online it seems that there is some type of metal I-beam supports that are commonly being used on top of the beams and before laying a plywood floor, but I am not sure exactly what kind or where to find them.

The ground level will need to have as much shelving everywhere as possible, so either possibly built into the lower parts of the pallet racking or as smaller free standing shelves.

Here are some quick photos trying to show some of the options if I were to be using the pallet rack shelving or the shipping containers.

Looking for any advice on building a mezzanine level in a warehouse space, to then use the second floor as a completely open and light working area, with all of the storage and heavy items down on the ground level.We are about to start moving into a small (1000 sqft) warehouse/workshop and needing to figure out the best way to build a full second floor mezzanine for the place that will also be level up to the top of an existing 9ft tall office room and a bathroom.The two options that I am looking into are either using pallet rack shelving as the base underneath to support everything, or to possibly bring in a couple of 20ft shipping containers and try to build the second floor on top of them, or maybe even a combination of both for the front half and the back half of the area.If using the pallet rack shelving, by building multiple separate free-standing shelves placed front to back, what would be the best way or best material to use to connect them all together with some kind of cross member support laid on top, to also act as floor joists for the second level, and that would be able to go across all of the beams perpendicularly?From looking online it seems that there is some type of metal I-beam supports that are commonly being used on top of the beams and before laying a plywood floor, but I am not sure exactly what kind or where to find them.The ground level will need to have as much shelving everywhere as possible, so either possibly built into the lower parts of the pallet racking or as smaller free standing shelves.Here are some quick photos trying to show some of the options if I were to be using the pallet rack shelving or the shipping containers.