I'm trying to make a script that allows me to customize HP for buildings. However, I still don't know how to place Image or Hudtxt on top of the objects.
You cannot (easily) place a text HUD on a map location due to the fact that HUD texts are HUD (head-up display) texts, and not map texts.
That means that you'll have to move the HUD text on the screen depending on where the player is standing.
Many attempts have been made and I'm fairly certain somebody uploaded their attempts somewhere on this website at some point (although I wasn't able to find it).
As for images, those can be placed on both the screen and the map.
Refer to image to learn how to place an image on the map, as there are examples on how to do so.