Do you mean the placement at a certain position?
If so:
System->create object at (x + MouseX - MouseX % 32,
y + MouseY - MouseY % 32)
where (x,y) is equal to the placement of your image's hotspot
If you meant limiting the placement area then just add a condition to your event that ignores input from the mouse when it is within a certain area.
System->compare (MouseX > 100)
System->compare (MouseX < 500)
System->compare (MouseY > 100)
System->compare (MouseY < 500)
You could also "cheat" and place a sprite in the area you want to limit construction to. Then use the condition:
System->Mouse is over sprite
I apologize if anything's wrong. My excuse - I started working with construct for the first time in several months yesterday.