If you could post pictures that would help, also make sure of your building's codes/rules, keep in mind weight, drainage, exposure (sun/wind/light), privacy concerns, lighting, etc. and consider getting professional design help for someone who specializes in roof gardens. You don't have to do everything all at once but a design professional could help you clarify your vision and give you ideas you may not have even thought to incorporate. Best of luck, 800 sf of outdoor space is wonderful. Don't forget you've got to get everything up to this space too.

dimensions or picture of current passage to balcony and balcony will b helpful

I would suggest you to cover some part or whole of the terrace floor with artificial grass. It stays green all year round and is also very easy to maintain as compared to natural grass. However, leave the place where you plan to install BBQ basin as it may get damaged because of fire. You can even place a swinger and 1 or 2 garden table set.

Harsha, You may want to go for proper terrace gardening and barbeque setup . Nice colour on the exterior !