I'm making an educated guess that $1000 Singapore dollars? is about £500. So I would go with something like this:
CPU: Intel Core i3-4130 3.4GHz Dual-Core Processor (£79.19 @ Aria PC)
Motherboard: ASRock H87M Pro4 Micro ATX LGA1150 Motherboard (£58.76 @ Amazon UK)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory (£59.98 @ Amazon UK)
Storage: Crucial M500 240GB 2.5" Solid State Disk (£82.99 @ Amazon UK)
Video Card: MSI Radeon R9 270 2GB TWIN FROZR Video Card (£131.98 @ Scan.co.uk)
Case: Corsair 200R ATX Mid Tower Case (£39.95 @ Amazon UK)
Power Supply: XFX 550W 80+ Bronze Certified ATX Power Supply (£44.08 @ CCL Computers)
Total: £496.93
To give you some food for thought. The case is personal preference, I just picked a popular one. The i3 is the best power house for your budget, that Asrock board is very well regarded. As for the graphics card, so long as your monitor is 1080p it should be able to play anything at high / ultra and will definitely have no problems with DOTA 2. Also I have gone with a single, decent sized SSD for maximum performance with a bit of a space compromise for your budget. Not sure of the availability of parts in your country but just an idea!