• you need following documents 
  Certified copies of land records specifying the title and ownership
• Certified copies of the land map (from Tehsil/Taluk Office)
• Certified measurement plan of Land Survey (from District Inspector of Land records)
• Copies of layout, site plan and building plan which should be duly signed by an architect
• Appointment letter of Architect and Registration Certificate of Architect
• NOCs from authorities (as applicable - Grama Panchayat/ Municipal Corporation/Highway authority/ Pollution Control Board (for industrial)
• Certificate from Patwari/ Talati that land in question is not under acquisition by government
• Record of Rights and Tenancy Certificate (RTC)
• Mutation letter
• Original sale deed
• Latest paid tax receipt

It is necessary otherwise there could be dispute in future.

For OC authorities would check whether construction has been done as per sanctioned plans 

It has to have the sketch with the order without which it can't be termed as legal. Oc is finally received after all legalities are completes by builder for said project

No, OC will not be given without checking

If order of conversion specifies location of land than sketch is not necessary. OC dose not confimr due conversion but only construction, no violation of buildign bye laws.

You can go ahead with purchase.

Dear Sir/Madam,

It is suggested that  as per your input, the property is fit to be bought. 

No.

As a large part of the land in India is still farmland. This is why revenue authorities issue a conversion certificate, stating the change in land use from agricultural to housing. A no-objection certificate should be obtained from the tehsildar's office for this conversion.

OC is given for the completion of the construction as per norms and rules in this regard.

OC has nothing to do with the conversion certificate.

- If the said conversion order is for the said property which you are going to buy having details of the property , then sketch is not mandatory. 

- However , you can check the details of that property from the office of Revenue . 

- Occupancy Certificate is obtained after the completion of the construction. It is important at the time of buying a property, seeking a home loan, before the builder allows people to take possession of the property and, for the transfer of Khata. This Certificate certifies that the project is ready for occupancy.

The OC is issued only once the building has been completed in all respects and can be occupied.

It is important as the details ie the map is important.

Everything is checked by the authority but you should verify everything and don't rely on authorities as builders give bribes.

Conversion sketch is not required.

Only a layout map approved from authorities is required for getting OC for building.