The Cisco 2800 series are part of the Cisco enterprise family, so you might be better asking over at:
https://community.cisco.com/
Although the 2800 series is still a current product its getting pretty "long in the tooth now". You might want to consider the newer Cisco 9100 series APs.
In the Meraki family a lot of my warehouse customers use MR74's. They are IP67 rated so don't mind an environment that's a bit dirty and they use external antennas. They are a 2x2 AP. They are a good fit for low data requirements like scanners.
https://meraki.cisco.com/products/wireless/mr74
Another option of merit is the next model up, the MR84. It's also IP67 rated but has a 4x4 radio so it will handle more challenging RF environments and is likely to deliver higher data rates. Note that it does need 802.3at power so make sure your switches can deliver this and have a PoE budget to be able to power all of the attached APs.
https://meraki.cisco.com/products/wireless/mr8
The closest match to the 2802i and 2802e series AP would be the MR42 and MR42E.
https://meraki.cisco.com/products/wireless/mr42
https://meraki.cisco.com/products/wireless/mr42e
External antennas can push the price up quite a bit, and sometimes it works out better using more APs with integrated antennas (like the MR42).
If you were using the MR42E and mounting on the roof seems reasonable and possible, then you could consider using this downtilt antenna. It is designed for mounting on roofs up to about 7.6m high pointing down (so it focuses most of its energy down rather than sideways).
https://meraki.cisco.com/products/wireless/antennas-power#MA-ANT-3-D5
As a quick rule of thumb I like to allow each AP to have a coverage circle radius of 15m. That gives good connectivity. I make that to be about 706 m^2. So in your case that comes out at about 4 x APs required.