Why did Moshe add the 'Hey' in "ha'Mishkan" and in each of the subsequent Keilim?
Ramban: He was (merely) 1 hinting at the detailed instructions that he would ultimately pass on to Betzalel and the workers. 2
Bearing in mind that now he was speaking to the people at large (Ramban).
See Ramban, Sh'mos 36:8, for a broader explanation as to why on some occasions the Pasuk gives all the details, and on others, only the general instructions.