It depends on how tall the person with the ladder is. Height + raisin height =3.3 meters is enough. The ladder can be reduced by 10 cm (0.1 m) if the head is considered not to touch the roof. So: height + ladder =3.2 meters.
Now the electrician special ladder is generally done with fiberglass, light, handling is very convenient, Hebei Shijiazhuang Jingzhong electric power technology Co., Ltd. production insulation ladder, you can search online.