"Creative office space costs us about $15 to $20 per SF to create," says Lincoln Property Co SVP Kevin Hayes. For a building with a 7.5% cap rate, that adds $40 per SF to the value of the building, but he stresses that the addition is only theoretical. "What we've seen is some of these creative tenants move out before the end of the lease," he explains. Another challenge for office landlords has been an erosion of rental rates for renewals—over the last year, he's seen rents slide a little for renewals.