Hi Ming,
You can create BDT object using TC BUS0 or CAWM. You can add custom fields or section of fields in SAP standard screen. Normally we are used this process whose custom user exits are not available. Please follow the following steps:
1. Design your custom screen using TC SE80 and SE51.
2. Declare PBO and PAI. Called BUS_PBO and BUS_PAI respective process. Active the object.
3. Go to task menu using TC BUPT.
4. Create application for your custom screen using TC BUS1.
5. Create data set( TC BUS23) and fields group (TC BUS2).
6. Create view( TC BUS3) assign fields group which is previous created.
7. Declare section and screen using TC BUS4/5 and assign respective object.
8. Create screen Sequence and assign sequence and categories.
9. Create divisibility using TC BUSD and choose your requirement option.
10. Active and checking BP transaction code.
Thanks
Apurba