Building:

It is forbidden to build anything during Chol Hamoed. This applies even if it is for the need of the Moed.

Meleches Hedyot: It is permitted to perform amateur building jobs on Chol Hamoed if it is being done for the sake of the Moed.

May a gentile continue renovations in one’s home during Chol Hamoed? No. One must protest the gentile from doing so.

May one attach a Mezuzah to a door on Chol Hamoed? Yes.