In order to transgress the melocha of Boneh, a permanent structure must be made. This is because when making a temporary structure that is made to be disassembled, the two parts that are put together are not considered building one new entity. Therefore, even though it is forbidden to close up a hole in the wall, it is however permitted to open and close a door or window. Since these structures are made to opened and closed constantly, we don’t see their closing as becoming an extension of the wall.
There are however instances when even a temporary structure will rabbinically forbidden. For example, to hang a temporary hook on a wall which attaches with a suction cup, even if you plan on removing it after a few hours, will be rabbinically forbidden. The reason is that since the hook is just a way to allow you to hang something on the wall, the hook is then seen as have become a part of the wall. The fact that it has not been permanently attached will lower the transgression from being forbidden by the Torah to instead being forbidden m’dirabbonon

Rabbi Tzvi Aryeh Hyman, Mir Yeshiva
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