Warren Buffett just wants to grow some weed. Cubic Designs Inc., a unit of Buffet’s Berkshire Hathaway Inc., sent around a thousand fliers to marijuana dispensaries over the last few weeks, offering to sell them growing space to expand the number of plants they cultivate. Fliers read “double your growing space” in all capital letters and “grow your profits.” The idea occurred to Cubic Designs after a couple of pot growers approached them about warehouse its mezzanine systems. Warehouse space is growing scarce in Denver, driving up rent prices. “We sold a few mezzanines in that market and decided internally, ‘Why don’t we do some marketing?’” said Shannon Salchert, the company’s marketing coordinator.