If its regular chicken wire, thats a poor choice for the screening. For a number of reasons, it has incredible potential to hurt the chams feet.
I'd investigate the use of some sort of plastic for the flooring, as it will be easier to work with, but thats me. Just be sure that the alloy you select is resistant to corrosion from water, as there are some formulations of aluminum that are not.
Pressure treated lumber contains arsenic, which in addition to requiring some special handling when cutting and drilling, especially indoors, always seems like a bad idea for a cham cage. Use untreated lumber, and finish appropriately.
I'm not sure what you mean by being able to walk in the cage, as its going to need to be elevated for any kind of drainage solution to work.
Remember you're going to need probably 2 feet of stand at least to provide clearance for your drainage bucket, and a foot or two above the enclosure for lighting. Assuming 8 foot ceilings, I would measure carefully to ensure that you will have enough room for everything.