SQL Server Database size - doubled running DBCC
CHECKDB by design will use tempdb space for temporary storage and it will fail if you run out of space. Make sure you presize your tempdb. You can check how much space it needs by issuing WITH ESTIMATEONLY command:
DBCC CHECKDB ([WideWorldImporters]) WITH ESTIMATEONLY;

You will be able to get an estimate space requirement for tempdb:
DBCC results for 'WideWorldImporters'.
Estimated TEMPDB space (in KB) needed for CHECKDB on database WideWorldImporters = 1.
Estimated TEMPDB space (in KB) needed for CHECKDB on database WideWorldImporters = 261556.
Object ID 1179151246 (object 'Warehouse.ColdRoomTemperatures'): The operation is not supported with memory optimized tables. This object has been skipped and will not be processed.
Object ID 1211151360 (object 'sys.memory_optimized_history_table_1179151246'): The operation is not supported with memory optimized tables. This object has been skipped and will not be processed.
Object ID 1243151474 (object 'Warehouse.VehicleTemperatures'): The operation is not supported with memory optimized tables. This object has been skipped and will not be processed.
DBCC execution completed. If DBCC printed error messages, contact your system administrator.

Since you have close to 800GB, what you can do is breakdown the CHECKDB into multiple DBCC commands. You can follow the recommendation here.