Typically, you'd
- visit the old site before things are removed to see their process and equipment
- visit the new facility and make your own sketch or take good enough notes to make a layout drawing of the space, doors, point of utility service connections, etc.
- meet with the client to determine their idea of a good layout.
- give them simple drawings of multiple layouts, no less than 3, to determine their priorities and ability or willingness to pay the costs for attaining the layout that they can convince you will give them the most productive or cost-effective layout.
- produce a full set of scale drawings of your optimized layout, including electrical power one-line drawings, plan views of electrical equipment, mechanical (HVAC, plumbing, compressed air, etc).
Some engineers that do building construction type drawings also meet with owners representatives to review contractors bids, evaluate construction work during progress and prior to final payments and acceptance of the new installation, and if needed with AHJs if building or occupancy code issues arise.
The level of detail in any of your work and produced drawings, specifications, equipment schedules etc. is between you and your client: if they wish to select contractors that they have experience and business relationship with, they may only want minimal detail, but ask you to review mark-ups, contractors drawings, or ongoing work or RFIs. They may ask you to provide detailed drawings suitable for review by authorities and open bidding by contractors to build "to plan and spec".
What I say here should simply confirm or summarize your own experiences. At least until recently, I've had textbooks around which had similar summaries. "Lean" practices, "design-build" contracts and "fast track" construction methods have become commonplace over the last 20 years or so, but essentially are modifications of the simple outlined process each with its own goals and advantages.
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Me wrong? I'm just fine-tuning my sarcasm!