@Jhon-Piñeres
The answer is probably found elsewhere since you asked your question, but because this was the first thread i found i think i post my solution here:
Command for shutting down:
shutdown /s /t 120
I choose 2 Minutes because thats the a longer time i need to leave but so normaly enough time to stop if i forgot something.
Off Command:
shutdown /a
Now i can tell my alexa to shut down my pc, by switching on shutdown, but i have also 2 minutes to cancel the shutdown by telling alexa to turn off shutdown.