Hi Abira,
If you do the deploy via Lifetime, you have zero downtime, don't need to show a maintenance page. Why did you need to use this approach?
But, in every case, are you talking about a reactive or traditional application? The target environment, is production?
In reactive you can set that page as Homepage, but you will need to go to the target environment and change it. In traditional you can set that page for your default EntryPoint (and need to change it in the target environment).
Hope this can help.
Best regards,
Ricardo M Pereira