A custom furniture designer who bought a Fulton Market District building more than 20 years ago to serve as his showroom has put the property up for sale, hoping to add his name to the list of longtime property owners in the trendy neighborhood cashing out with tidy profits. Designer Morlen Sinoway confirmed he has hired Chicago brokerage Greenstone Partners to sell the 15,000-square-foot building at 1052 W. Fulton St. The asking price for the three-story brick building one block west of Google’s Chicago office is just under $600 per square foot — or nearly $9 million — in line with the sums per square foot paid for other Fulton Market properties in recent years.