Active Directory - create root domain

This can be done through PowerShell script - as below:

Import-Module ADDSDeployment
Install-ADDSForest `
-CreateDnsDelegation:$false `
-DatabasePath "C:\Windows\NTDS" `
-DomainMode "Win2012R2" `
-DomainName "contoso.com" `
-DomainNetbiosName "CONTOSO" `
-ForestMode "Win2012R2" `
-InstallDns:$true `
-LogPath "C:\Windows\NTDS" `
-NoRebootOnCompletion:$false `
-SysvolPath "C:\Windows\SYSVOL" `
-Force:$true

or using GUI:

Exchange 2010 and Active Directory 2012R2 - compatibility

Just to remember:
from Paul Cunningham blog
from Technet web site
Exchange 2010 is no longer a blocker for 2012R2 domain controllers - with SP3 and RU5 of course