I had a Firm looking for Cost Estimating services ask two (2) questions: I will post my discussion on both topics.

Answers to your questions:
1. Provide a technical narrative detailing how you would develop a cost estimate for a 90% set of multi-trade construction documents with a construction budget of $2.5 million. In your narrative, identify manpower hours to produce your cost estimate.
Utilizing 90% design drawings with multi-trade estimates would be handled in this manner:
With 90% drawings, assuming all trade estimates have all the details to estimate with and there should be minimal contingency. I used to use the 1-3 hour per page (Estimator Judgement) methodology (based on how detailed each drawing is) to give estimate hours for proposals. It worked well until BIM models furnish quantities now, which saves hours. Utilizing a software tool that has RS Means data as a starting point to pull into cost estimates.
If the estimators are in a production setting, then I would use all trade estimators and have each only focus on their trade and have a merge of estimates into the final delivery.
If these estimates have no deadlines, one estimator could perform with all the hours suggested below. This isn’t an exact science but with years of experience you get the hang of it.
A sliding scale would have to be determined if the project size is small enough for one (1) estimator or multi-trade estimators. Depends on the size of the project. For example: All of these scenarios assume durations and disciplines of work are equal.
• Projects < $1M to 5M 1-3 Estimator Duration: 2 weeks
• Projects < $5M to 10M 1-3 Estimator Duration: 2 weeks
• Projects $10M – $25M 3 Estimators Duration: 2-3 weeks
• Projects $25M – $100M 3 Estimators Duration: 3-4 weeks
• Projects $100M – $500M 6 Estimators (PMO) Duration: 4-6 weeks
• Projects $500M – $1B 6 Estimators (PMO) Duration: 4-8 weeks
Note: Project that are this large may estimate in Phases or 2 teams of multi-discipline estimators. $500M to >1B would require a PMO office and teams of estimators, PM’s Engineers, Schedulers, Project Controls, etc.