Need some advice on Flat Agrreement

Hi Sir, I am planning to buy new flat. But when I read agreement given by Builder it has some clause mentioned below. I want to know is it common practice and should I buy this flat or not? 1. IT IS ALSO UNDERSTOOD AND AGREED BY AND BETWEEN THE PARTIES HERETO that the terrace space above the said building, if constructed by the Promoter at their discretion shall not be a common area but shall belong exclusively to the Promoter or to the Purchasers of the units to whom the same will be allotted by the Promoter as per Promoter’s discretion and the said terrace space is intended for the exclusive use of the respective flat Purchaser. The said terrace shall not be enclosed by the said unit Purchasers till the permission in writing is obtained from the concerned local authority and the Promoter or the Society and/or Association of Apartment Holders as the case may be. The Promoter or its assignees shall have a right to construct units, etc. on the said terrace towards FSI of road widening area, FSI of internal roads, TDR or any other FSI. 2. The Promoter may allow display of advertisement and/or hoarding sites/neon signs, or may allow erection of antenna or for cable/satellite television, wireless, paging, mobile, cellular services, on the building and derive appropriate income therefrom in its own rights. The Promoter shall be entitled to erect hoardings on the property and/or said building and to sell or let/lease the same and to receive income thereof and the property will be conveyed subject the said right of the Promoter. 3. The Promoter may allow to install Solar Water Heating System / dish Antenna System for the use of the Unit Holder at a designated place to be decided by the Promoter. 4. It is specifically agreed between the Parties hereto that even if before completion of the entire scheme “Rajveer Galaxy” or sale of all units should the Society and a Apartment Deed be registered, then for the unsold premises shall not be liable or required to contribute towards the common expenses or maintenance charges or any amount any head. Thanks, Shashank