What is the ruling on one who shortens his hair completely, taking more from the sides due to the rapid growth of hair in them, knowing that he shaves monthly in the same manner?

Hair should be cut evenly, because cutting some of it shorter than other parts falls under the category of qaza', which is forbidden. This is supported by the Prophet's (peace be upon him) prohibition of qaza', and his command to either shave the entire head or leave all of it. Furthermore, cutting some hair shorter than other parts falls under imitating the corrupt and adopting the practices of the Majus (Zoroastrians).