Thanks to Frazzle, this one works for me,
Code:

---

function create_objects()
{
var distTrace;
wait(1);
c_setminmax(me);
my.polygon = on;
vec_set(temp, my.x);
vec_sub(temp, vector(0,0,1000));
trace_mode= ignore_me | ignore_passable | use_box;
distTrace = c_trace(my.x,temp,trace_mode);
	if (distTrace> 0)
		{
  		 my.z -= distTrace;   
		}

}

//example function
function place_object2()
{
   temp.x = 200; // place the object 200 quants in front of the creator
   temp.y = 0;
   temp.z = 0;
   vec_rotate (temp, player.pan);//be carefull to set "current_player" to your player name.
   vec_add (temp, player.x);
   ent_create(object2_mdl, temp.x, create_objects);
   
}  

---

Just enable polygon collision in properties or by script on your model terrain (I always use model terrains)