Cost estimation is a dynamic and knowledge intensive process. Current practice of construction cost estimation is a process with fragmented knowledge. In order to have an integrated process, semantic should be modelled in respect to pragmatic. The investigation of BIM-based cost estimation confirmed that IFC can provide construction project semantics but incapable of relating domain semantics and pragmatics. In order to overcome this gap, we adopt organizational semiotics to fully reveal semantic units of cost estimation from a process perspective. Pilot study confirms feasibility of this approach. Future research will be a case study to collect all the instances for semantic units. Then semantic consistency and pragmatic implementation should be realized by the applications. This research highlights the importance of alignment between semantic (domain ontology) and pragmatic (meaning in use), it contributes also to identify a new approach of knowledge engineering for construction professional services under BIM environment.