the upper part having vertical ridge 82 for holding and turning said base 81 nail 83 at the lower part which penetrates through a pre arranged hole in roof sheathing 10 and screws down in hook 41 of auxiliary pole 4 being steadfastly hooked in said hook 41 through the resilient elasticity of roof sheathing 10 fig2 shows drain chain 9 which includes locating bar 90 shown in fig2 and bucket 901 shown in fig2 and 27 drain chain 9 is constituted with one drain chain head 91 having adjusting wings 911 just at the upper and a number of drain chain rings 93 connected with one another adjusting wings 911 are used for changing their own height in the bottom hole of bucket 901 each drain chain ring 93 is provided with connecting notch 92 having an inclined tip end for connecting with the neighboring drain chain ring 93 at the upper or the lower part so that each drain chain ring can be united with each other to become a long drain chain 9 reaching the ground bucket 901 is placed just under outlet 20 of rear beam 2 and at the top of drain chain 9 so as to let the collected rain to flow down along said chain 9 without splashing around bucket 901 is provided with an oval hole at its bottom for adjusting wings 911 of chain head 91 to insert in and to be turned for 90 degrees so as not to fall off bucket 901 locating bar 90 is to be set on the upper edge of bucket 901 and to be united with drain chain head 91 in order to prevent said head 91 from turning and falling.