What construction lvl is a must?

I'm slowly only training construction through quests and tears of guthix. I just can't bring myself to spend a lot of gp on making something to then get rid of it after later lvls (imma pretty broke so all my gp is going to training slayer to hopefully not be pretty broke). What lvl do I need to get in construction to start building a genuine game must? I feel like my question might be way confused so sorry if it is 😂😂