Those boxes piling up on your doorstep over the holidays don’t ship from Santa’s workshop. As Americans spend more money shopping online, real estate developers are sinking record amounts of money into new warehouse space, building bigger, taller structures to meet the needs of e-commerce — and the robots that help it along.

The first thing online clothing reseller ThredUp did after clinching a new round of funding last year? Hunt for strategic warehouse space to get the goods to customers as fast as possible.