Question About Cost Planning for Industrial Steel Structures

Hi Alyana, even though I do no work in the construction industry, the estimating methods are basically similar, only the materials and weights change.
I start with the original Request for Quotation from the customer which usually gives the basic details of what he wants.
Depending on what support from Design, (if any) and, naturally, your own degree of expertise, you can generally work out what the dimensions are, how long is the building, how wide, how high to roof level, How high are the steel trusses, how many uprights are needed etc.
Are the uprights & Crossmembers just supporting the roof or is there a need for an overhead crane ?
Once you have worked out roughly how much steel you need, H-section or L section for Roof trusses, Cross braces etc. do a rough estimate detailing on what your estimate is based, how many running meters, what section you used.
Any other costs for secondary work, drilling and bolts or welded joints. Additional costs for cranes and other equipment like weldingmachines. manpower etc.
This is your first basic estimate, do not ever change it or amend it.
Any subsequent changes must be detailed with regard to what changed from the previous estimate and the subsequent costs added (rarely subtracted ) from the previous estimate.
Always use a suffix to your estimate with a date, that way you can always go back and say that Design / Material / Assembly changed and cost x amount. Traceability, record who requested the change and who signed off on it !!
Always make sure everybody involved in the Offer / Bid is informed about any changesto Design / Cost.
That shows accountability, so nobody can come later and say you didn't tell us about the changes or the cost implications