Hi Andrew,
The design depends on many things. Such as what you want to achieve. (i.e. do you want voip level coverage or just data coverage, RFID tags?) the characteristics are of the warehouse (i.e what physical obstructions are there like rack shelving, what goods are on the shelves, how high the ceilings/racks are) plus the end user device considerations - the devices in use in a warehouse are typically old clunky scanners with antiquated radios that support old wifi standards..
Consider where you are going to place the AP's. If the warehouse has high ceiling then you'll probably want to use directional/patch antennas to push the signal down to where it's needed between the shelving/aisles. You definitely should do a passive survey in tool like Ekahau to see what the coverage looks like.
Regarding the end user devices, if they are old 802.11g/b devices then consider that this standard does not support multi-path (reflections) so you will need line of sight between the AP and the device. They also don't support 5GHz so you'll be stuck with the noisy 2.4GHz band.
There's lots more to consider. Perhaps if you can share a bit more detail then I could help bit more..
Regards,
Mark
Mark Ribbans
