To provide a building system for building an object, including a building apparatus that ejects a material of the object, a data generation unit, and a control unit. The data generation unit generates ejection position designating data based on input data indicating the object in a format different from that of the ejection position designating data. During a time when the data generation unit performs an operation of generating the ejection position designating data, the control unit causes a head to form a plurality of material layers constituting at least a part of the object, and sets a layer forming start timing for starting to form the material layers so that the interlayer time does not exceed an upper limit time set in advance. Hence, appropriately building a high quality object.