Gptgen

Gptgen is a command-line utility made to help you convert MBR-partitioned hard disks (MSDOS-style scheme) into GPT, the scheme used for GUID partition tables. It keeps all HDD data intact, so you dont have to worry about losing important files, such as Windows items.
Extended partitions are supported. Because the application cant tell the difference between primary and logical partitions, both types are treated as primary.
The syntax for this command-line tool is gptgen [, where device_path represents the full path to the device file, such as \.physicaldrive0.
As far as the arguments are concerned, you can instruct the program to write a backup of the original MBR to a specific file (-b , --backup file), build a GPT with nnn entries, where the default is 128 (-c nnn, --count nnn), or disable user notifications if a boot partition is found (-k, --keep-going).
In addition to this, it can preserve the existing MBR without writing a protective MBR (-m, --keepmbr), as well as write directly to the disk instead of separate files (-w, --write).
The help message can be displayed by writing the apps name without arguments, or by using the -h line.