After hiring a main contractor to rebuild my 3-storey house, I learned several valuable lessons that I'd like to share:

(1) It's advisable to engage an architect who can handle the engineering and interior design aspects.
(2) Unless you're willing to pay a premium to a reputable construction firm, it's better to let your architect manage the project and hire individual suppliers for different tasks.
(3) A lump sum project may seem more convenient, but it's not always cost-effective or quality-assured. For instance, when I needed metal fabrication work done for items such as awning, handrails, rain sump covers, and I-beam staircases, I realized that splitting the job among three suppliers saved me about 20K, as each one had different strengths and pricing.
(4) If you decide to award the entire job to one main contractor, make sure to sign a formal contract that specifies the penalty for any shortcomings such as late delivery or poor project management. Otherwise, you may end up having to act as your own project manager, like I did for the past 1.5 years.
(5) Invest in electrical engineering consultancy to get accurate drawings and ensure that the electricians follow them strictly. Don't rely on the main contractor's experience or shortcuts. Most of electricians further subcontract to foregin labours.
(6) Have your plumbing pipe drawing ready before starting the work, and be specific about the materials (poly, stainless tube, PPR, and etc) and sizes to be used.
(7) Don't choose your contractors based on the lowest cost alone. Many contractors make money from variation orders, so it's crucial to have your architect deliver the scope of work, specifications, qty and monitoring. I made the mistake of choosing my main contractor solely based on cost, but it turned out to be more expensive due to rework and wastage.