Short answer: Turnkey = pay when finished. Land and build = buy land, build in stages. Turnkey simpler for first home buyers.
Turnkey means you pay when the house is finished and ready to move in. Land and build means you buy the land first, then build in stages, paying as construction progresses. Turnkey is simpler. Land and build gives more control but more complexity and risk. First home buyers usually prefer turnkey.
Turnkey: $600,000 total, pay at completion
Land And Build: $250,000 land + $350,000 build
Land And Build Finance: Progress payments during construction
Recommendation: Turnkey for simplicity