by recording at 1080p do you mean Casino mode or just with normal compression?
we have a site that's approaching 100 cam's all running at 3mp (higher than 1080p) and when you limit the bandwidth to 4096(we tend not to notice a difference vs running higher bitrates) we find they do around 40gb a day per cam on average (we have a fair amount of motion, but nothing like an intersection) I assume your customer wants Rack mount in the following.
you more or less have two options, you can either spend big bucks on a single large name solution, or go how we did, just run Multiple Servers (we split the VMS's over multiple virtual machines, and then on multiple servers) then run multiple Synology NAS devices.
your garden variety rack mount unit will hold 12 drives, each of those main units will handle 2 expansion units, which is another 12 drives, fill them with 8tb drives and you are talking 288tb of unformatted storage split it up into 4 x 8 drive arrays in Raid 5, with four hot spare slots and you have four ~50 TB arrays, if you assign a virtual server to each array, with short term storage on each Virtual machine (we use WD raptors) then you'd have around 40 days on 20 cam's per virtual machine...
expand/play with numbers as required, be warned, no matter your solution unless you go a crazy expensive solution you are going to experience the occasional array failure... I've seen a single drive going nuts take out a whole array a few times, I've seen bad controllers take out whole arrays etc
Deep storage is not particularly useful unless you know exactly how far aback you need to find the storage, and a VERY expensive fish to chase.
Synology + 2 x External expansion units: $6.4k
8tb disks $345 ea $12.5k
So for around 210tb of Long term storage you are looking $20k aud, and that's not bad at all compared to the big guy.
Server wise we can get Used DL380 Gen8's with a pair of 8 core processors for $4k, throw in a pair of boot SSD's ($300 ea for intel S3610) then a set of local storage drives for $400 each and your talking $7k for a server ready to hold between 40 to 60 cams
you guys in the states should be able to smash that pricing.
over view wise, I don't like going big single boxes, the prices does not go up with performance, and if something falls over EVERYTHING is down vs just a small pack of cam's.