Here I disclose one past Estimator's Bid errors that can be avoided by other Contractors. 

The following example describes a mathematical problem; for simplicity, the sample dollar amount is quite small, and percentages are examples.  All may vary per Bid and Contractor.

This Contractor's Estimator calculated costs of construction jobs in order to bid them.  This calculation is for materials, labor, transportation and overhead, as seen on blue prints, other drawings and specifications.

   Material is:  fixtures, conduit, boxes, wire, switches, wire-nuts, wood or metal supports, etc.
   Associated assembly labor might be 10% and profits might be 15%.
   This Estimator would therefore add 25% to the materials cost.    1st incorrect step 
        (15% profit is really of the final sold price.)

A Bid Example:
These small sample materials came to $20,000
The Estimator’s 25% addition is  $5,000.
Therefore $25,000 is used to bid this job.    ERROR

Won a Bid:
When awarded a Bid, the Contractor buys ALL the materials at $20,000 for inventory.  The Contractor’s financial management people are alerted to take 25% of that Bid’s payment(s): use 10% toward the labor and overhead, and 15% toward profits. 
They’re told the remaining 75% goes toward material inventory.

Note the example shown is a single payment.  In large Bids, the Contractor’s money is received in payments based on completed phases; i.e. per floor in an office building or parking garage, etc. 

The Percentage Problem:
Remember that $5,000 was added to the materials cost of $20,000.  Now management takes 25% * $25,000 and has $6,250 to distribute as mentioned above.   2nd incorrect step 

Note that $6,250 - $5,000 = $1,250 removed from the materials’ required payment.
This process leaves $18,750 to pay for the materials, rather than necessary $20,000 to repay the materials supply.

Wrong Math In Use !
The Estimator used an improper formula for Mark-Up, it was not correctly calculated from the very beginning, and made materials payment deficient.  This example is for a mere $20,000 job, and
you can imagine how critical a multi-million dollar Bid can be.

This occurred for most years, for every job.  In bidding, they sliced every cost as low as practical, which is fine.  The miscalculation was a cost Mark-Up when they are bidding, therefore percentages against the earned Bid money (sales price) couldn’t properly pay what they owed.  Financial management didn’t realize the materials cost percentage of the initial Bid.

When that job was done, materials weren’t fully paid for, and those required money from the next job.  I have since learned of several Contractors with this same error, and failure. The learning solution is even more important when LED products are so much more expensive. 

I disclosed an error but no specific corrections because some are different and many know the way. 
If you need help, I can show you valid solutions, and save you from those losses.