I dont really understand what do you need...but maybe this helps?
draw_self();
draw_rectangle_color(0,0,room_width,y-1,c_black,c_black,c_black,c_black,0);
draw_rectangle_color(0,y+sprite_height+1,room_width,room_height,c_black,c_black,c_black,c_black,0);
draw_rectangle_color(0,0,x-1,room_height,c_black,c_black,c_black,c_black,0);
draw_rectangle_color(x+sprite_width+1,0,room_width,room_height,c_black,c_black,c_black,c_black,0);