Melachim Aleph, Shlomoh has become king, but Beit Hamikdash has not been built. It records that "the people continued to offer sacrifices at open shrines" as did the king. The Tanach does not record that either king, prophet or statement of G-d indicating this is wrong. There is no statement that the sacrifices were in secret and I assume the altars were within requirements of Torah (no cut stones) so I assume it was acceptable to G-d. Since this activity was before the building of the House like the time we live in now, should we do the same thing - provided - it follows the requirements of Torah? Is G-d waiting for us to do so?
The Mishnah Zevachim 14;8 and Mimonides Bet HaBechirah 1;3 explain that there were times in history when sacrifices and private alters were permitted outside of the main place of service, but after the temple was built in Yerushalaim – there's no other place but the alter on temple mount we are allowed to offer our sacrifices.