In fact, it is usually best to spend the time to seek out and communicate with contractors who have already built such projects. For the purpose of this conversation we will consider the costs and requirements for the construction of a greenhouse on a residential lot.According to the Craftsman National Building Cost Estimator program, the pricing on a greenhouse measuring 12'x12' would be around $3587, or $25 per square foot. This might be problematic in areas of heavy frost, however); 2  Concrete-the knee walls and flooring of the greenhouse would demand roughly 3.5 cubic yards of concrete. 3  This is priced at an average of $75 per cubic yard, and with labor would cost around $540;