3D Solid Model Creation of 2x Silos

Hi, I require someone to create a 3d Solid model of 2x Silos, I don't care what CAD system is used to create the 3d solid models as long as I can receive a STEP file that can then be imported into Siemens NX.
The Model must be dimensionally correct.
The model is going to be added into a Plant Layout, so the interfacing areas need to have holes added.
Inner Cone area can be modelled as basic, no need to model individual plates
Outer Silo can be modelled as Basic, no need to model individual plates
Staircase, all Handrails, Stanchions, Supports need to be modeled, but can be done as basic Models.
All drawings attached can be be supplied in 2d .dwg format.
can discuss more information on award of project

Regards
Sean