4U server will be monstrous..- would I buy it? well, no.. - PSU as usually loud, server parts are overly expensive & not needed for such buid =)
remember the fact that 4x TitanZs iare (4x3) 12 Slot spacing..no regular (tax, eats) motherboard without ribbon cables or backplane is going to be capable in housing those.
WaterCooling is not a problem, You can make drainage system & take of Your liquids, re-fill could be done using distilled water, that You can buy in any automotive shop - they sell that for pouring into car batteries =)
4x TitanZ with EK tops should take 8Slots, instead 12 if You go air-cooling route & that (8slot configuration) should fit into any case that have some extra space for rads or You can use "regular box" & quick disconnects to add 9x120/9x140 rads for proper cooling capacity.
Don't forget that for 4x TitanZ You probably need dual power supplies as there's no change even 1500 or 1600W stable going to lift this ..You might end up running (as Octane don't need that much under load), but stability would be guaranteed =)
If You need some help, have predefined budget or any other guidelines, drop more info & we can try to find some solutions =) like using let's say
DopoMiner (if You want to avoid water-cooling )