Brent Waller, designer of the LEGO CUUSOO Ghostbusters submission, has provided instructions to build the Ghostbusters Headquarters. This should hopefully satisfy those that were disappointed the firehouse would not be apart of the upcoming set. You will need to install LEGO Digital Designer and download the instructions here.
Here is what the actual firehouse looks like built and displayed next to other modular buildings.
Via Brent Waller at Eurobricks