One of the amazing things about Sri Lankan homes is that the huge majority of them are built using completely standardized building practices. One reason for this consistency is a set of uniform building codes that apply across the country. Another reason is cost -- the techniques used to build homes produce reliable housing quickly at a low cost (relatively speaking). If you ever watch any house being built, you will find that it goes through the following steps:

Grading and site preparation
Foundation construction
Framing
Installation of windows and doors
Roofing
Siding
Rough electrical
Rough plumbing
Rough HVAC
Insulation
Drywall
Underlayment
Trim
Painting
Finish electrical
Bathroom and kitchen counters and cabinets
Finish plumbing
Carpet and flooring
Finish HVAC
Hookup to water main, or well drilling
Hookup to sewer or installation of a septic system
Punch list
Many of these steps are performed by independent crews known as subcontractors. For example, the framing is generally done by one subcontractor specializing in framing, while the roofing is done by a completely different subcontractor specializing in roofing. Each subcontractor is an independent business. All of the subcontractors are coordinated by a contractor who oversees the job and is responsible for completing the house on time and on budget.