What would be the best method?

Okay, I would use an transparent image to check the collision and the read up on the function ImagesCollide()
But the wall pic, has to be seperate from the floor pic.

Then when the collision is met, stop mouse movement like.

x=MouseX()
y=MouseY()
If colided=False
   DrawImage(check,x,y)
Else
   MoveMouse colided_x,colided_y
End If
CheckCollisions()

And the colided_x&y would be set when the Collision Function returns true, to the values of the Mouse Position.