Let's make some simple calculation.

Steel price is coming down slowly already.
USD 700 to USD 650 per MT.

Cement still up.

If you delay your project by 1 year,

2023 Aug start build.
2022 Budget/cash in hand : RM500,000

Put in multiple source of investment which bring return about 10%.

2023 Aug : You will have extra cash

Budget : RM500,000
Investment return : RM50,000
Bonus : RM20,000
Extra saving : RM30,000
Your budget 2023 : RM600,000.

You need 1 year to have your house built up. You need to pay progressive payment through the year.

2024 Aug :
Bonus : RM20,000
Extra saving : RM30,000
Dividend income : RM20,000
Total income : RM70,000

I believe delay of project is better choice. You can use this one year ask for tender and negotiate for better deal.

Btw, hope you have your dream house done by year 2025.