The Google Play Store was out of Nexus 5 16GB stock a couple of hours after the device was officially announced. The 16GB units are still out of stock in the US Play Store. There are 32GB units available - both Black and White - but the bad news is if you haven't pre-ordered one already you're in for a wait. The Nexus 5 32GB in the US Play Store comes with the note "Leaves warehouse in 2 - 3...
Source: http://www.gsmarena.com/black_nexus_5_16gb_out_of_stock_others_ship_with_delays-news-7110.php