mkdir that overwrites any existing directory

You can delete the build directory with

rd /s /q build

or

if exist build rd /s /q build

I wanted to create directory only if it does not exist
If it exists, nothing to do

Below worked great in the bat file:

if not exist someDir1 mkdir someDir1

I don't think it is possible to use the mkdir command to do that natively (though if you were will to do a bit more scripting, it would be possible).

A simple alternative is the following command in powershell:

New-Item path -type directory -force

Where path is something like C:\users\name\build

For more on New-Item see: http://technet.microsoft.com/en-us/library/ee176914.aspx