Retail version of Windows OS is pricey, just go for OEM key if your friend doesn't have too much money for it.

Intel Core i5 6500 - RM 835
Gigabyte B150M-D3H (D4) - RM 379
Kingston 8GB DDR4 2133MHz Value RAM - RM 145
Palit GTX1060 6GB GDDRR5 Dual Fan - RM 1249
Kingston SSDNow UV400 240GB SSD - RM 265
WD Blue 1TB HDD - RM 209
Superflower Leadex Silver 550W - RM 339
Tecware Alpha - RM 199

Total: RM 3620 (ETech price inclusive of GST)

Left RM 400+/- for the OS, some people reported that some sellers (like ETech and Techview) will install the OS for you for free but I am not entirely sure on this, you can try to ask them for confirmation on this

Alternatively, you can look for Garage Sales for OS key but beware of counterfeit key.

To max out 4k budget without including the cost of the OS, you can either upgrade to i7 6700 or 16GB RAM or swap to another case etc.

Superflower is one of the best PSU manufacturers out there, so no worries on the quality.

Get Leadex Gold 550W at RM 409 if you aim for top tier PSU (tier 1), the low selling price makes it very worth to get now because usually we have to spend a lot in order to get a tier 1 PSU (typically > RM 600).

You can also look for Seasonic M12II EVO 520W/620W, price is around the same but it is a tier 2 PSU and rated with 80+ Bronze vs 80+ Silver/Gold on Superflower Leadex Silver/Gold.