Wendypooh
just my 2 cents worth. the 3 most important things in the house are
1. tiles (permanent fixture, must gel with everything else in the house)
2. lightings (down light & cove light, design of false ceiling, dining light all very important to create the right mood)
3. carpentry (look at the whole piece of laminate at their factory, not just that tiny peice of sample in the catalog)
Other things like
4. curtains (can enhance & soften the mood in the house, don't buy ready made ones that look like ready made ones)
5. Bathroom accessories (WC, designer basin, designer taps all help to elevate the class of your house)
Interior design is all about creating the mood.
By the way I'm not ID trained. I'm just a very involved owner who select every single item & design everything in the house

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Visit more condo show flats especially those in district 9, 10, 11. will give you a lot of ideas and inspirations. happy renovating !