Bangkok, is a very good place for budget but decent quality shopping! Here are some of my recommendations to must- visit for shopping in Bangkok!
1) Chatuchak Weekend Market
Chatuchak is one of the world's largest weekend market, with more than 15,000 stalls.
You can find almost everything here. Right from clothing, housewares, plants, to pets! etc...
Chatuchak is a must visit market for most tourists and locals too. Although the surface area of Chatuchak is huge, each categories of goods are nicely divided into different sections.
Open: Saturday & Sunday
6am- 6pm
(Recommended to visit from 9+am, where most stalls are opened and weather is not that hot yet. Afternoon at Chatuchak can be extremely scorching and warm.)
BTS: Mo Chit Station
MRT: Kamphaeng Phet Station
2) Pratunam Market
A major market for clothing at low price.
Located at the intersection of Ratchaprop and Petchburi roads (next to Amari Wategate Hotel extending
to Baiyoke Towers).
Open: 24 Hours
(Retail Shops open from 10am - 9pm)
3) Platinum Fashion Mall
Platinum Fashion Mall is made up of two malls side by side with no connecting walkways inside the building. Platinum mall A & B. It's a famous mall for both locals and tourist. Good for single buyers, but even better for wholesale. Their wholesale is minimum purchase of 2 -3 items. Must visit!
Mall A- 7 retail floors building with wide range of goods (mainly both female and male clothing, accessories, children wears.) Each categorized in different levels.
Mall B- 6 retail floors building (mainly foot wears, bags and clothing.)
Recommended visiting hours: 10+am/ 11am - 6pm
Location: on Petchburi Road of Pratunam.
4) Big C Supermarket
It's always worth visiting local supermarket for a view and experience of locals' daily life.
There are wide varieties of merchandise here. Love Thailand particular food product? Eg. Tom Yam Instant Noodle. Come and get it here. 
Slowly browse around with the cute basket. Dried/ packed food, daily necessities, cooked/ raw food, etc...
And among all the wide varieties of merchandise i would like to recommend the must buy!
TA- DA!! This is Thailand's famous sweet and spicy chili sauce!
It goes well with especially fried food. yum yum...!
The Big C Supermarket
There are many many outlets at Bangkok.
The one i visited- BTS: Chit Lom Station
Open: Daily 9am- 11pm
To be continued.. ( Coming up.. share with you the things/ food i thought that are worth trying/ buying in Bangkok.)
