A computer implemented method for creating a three-dimensional Ventilation, or Air-Conditioning mechanical system model, the method comprising: aligning a plurality of Ventilation, or Air-Conditioning mechanical systems drawings covering multiple interconnected floors of a building, each system drawing defining relationship between Variable Air Volume units and supply/return air ducts; extracting a plurality of Ventilation, or Air-Conditioning mechanical features from the plurality of Ventilation, or Air-Conditioning mechanical systems drawings; identifying a supply relationship between the plurality of Ventilation, or Air-Conditioning mechanical features by identifying a serving relationship between Air Handling Units and Variable Air Volume units; calculating supply requirements to support the plurality of Ventilation, or Air-Conditioning mechanical features by calculating paths for vertical ductwork for supply/return air ducts through multiple floors connecting Air Handling Units and supply/return air ducts or Variable Air Volume units; including projecting vertical ductwork onto a plurality of said floors; identifying, for each floor of said plurality of floors, a furthest Ventilation or Air-conditioning mechanical feature installation from the projection of the vertical ductwork and modelling ductwork between the vertical ductwork and the furthest Ventilation, or Air-Conditioning mechanical feature and creating a three-dimensional model of the plurality of Ventilation, or Air-Conditioning mechanical features for the multiple interconnected floors, the three-dimensional model defining the calculated vertical paths for vertical ductwork for supply/return air ducts on multiple floors connecting Air Handling Units and supply/return air ducts or Variable Air Volume units. aligning a plurality of Ventilation, or Air-Conditioning mechanical systems drawings covering multiple interconnected floors of a building, each system drawing defining relationship between Variable Air Volume units and supply/return air ducts; extracting a plurality of Ventilation, or Air-Conditioning mechanical features from the plurality of Ventilation, or Air-Conditioning mechanical systems drawings; identifying a supply relationship between the plurality of Ventilation, or Air-Conditioning mechanical features by identifying a serving relationship between Air Handling Units and Variable Air Volume units; calculating supply requirements to support the plurality of Ventilation, or Air-Conditioning mechanical features by calculating paths for vertical ductwork for supply/return air ducts through multiple floors connecting Air Handling Units and supply/return air ducts or Variable Air Volume units; including projecting vertical ductwork onto a plurality of said floors; identifying, for each floor of said plurality of floors, a furthest Ventilation or Air-conditioning mechanical feature installation from the projection of the vertical ductwork and modelling ductwork between the vertical ductwork and the furthest Ventilation, or Air-Conditioning mechanical feature and creating a three-dimensional model of the plurality of Ventilation, or Air-Conditioning mechanical features for the multiple interconnected floors, the three-dimensional model defining the calculated vertical paths for vertical ductwork for supply/return air ducts on multiple floors connecting Air Handling Units and supply/return air ducts or Variable Air Volume units.