Hi, Cougar. Welcome to the forums. The answers really depend on what type of equipment you expect to deploy. We just finished remodeling a small, traditionally (subfloor) cooled, general purpose data center. Today we're mostly using 1U and 2U servers and disk arrays, but we anticipate more blades and other higher density form factors sooner or later. Here's what I think:
Rack Depth: 1200 mm (48") - Allows increased equipment depth and in-rack cabling space
Cold Aisle Width: 1800 mm (72") - Increases air supply by 50% vs. 1200 mm aisles
Hot Aisle Width: 1200 mm - Provides adequate rear rack service area, aligns racks with floor grid to optimize subfloor access
Overall, since anticipating the future is an inexact science, expect to be wrong on some dimension -- space, power, cooling, cableway, floor loading, etc. Be sure to have a plan for 1) providing more of that resource when you run out, or 2) how to avoid running out.
A standard rack depth for traditional servers is 40 - 42 inches. If I were you, leave off the cable management arms...but do have cable management system in the rack!
I am just implementing blade racks and I will not use anything less than 48 inches. Unfortunately our networking team is dictating the use of pass-through network blades on the chassis so they can sniff individual servers...so I can have the potential of 102 copper cables in a rack with just 3 blade chassis....136 with 4 chassis...and then there are fiber storage lines....and power cables.
I've heard that two tiles should be your cold aisle and one tile should be your hot aisle. There are always pros and cons. Your cooling capacitiy and cooling distribution needs to be considered. Opening up a third row of tiles may allow too much air flow and create hot spots may occur in other sides of the data center (I've done that).
Aisle space is important, but there's no standard measurement because the space between aisles depends on the racks and cooling system you've employed. Ideally, to aid in cooling, you'll space racks at least four feet apart, increasing to six to 12 feet apart when power consumption exceeds 5 kW per rack. But this may be impractical in high-density environments. Hot/cold aisle configurations, implemented with CRAC units, let racks be placed closer together. Depending on your High Density cooling strategy will also add to the distance between the racks and ceiling heights. If you have low ceilings you may want to have a larger hot aisle as well.
Remember that the wider the corridors are, the less footprints you will be able to put in place. So less ROI as far as space is concerned.
Lock the cold corridor down as much as you can (place doors and roofs), more than 100cm rack depth is -in my opinion- a waste of space and air pressure. Keep the pressure under (the floor) as high as you can and put blinds in every unused unit.
Furthermore, let customers pay for used power instead of default power use (lets them buy low voltage units).