Don't buy a big new efficient miner for this for one it will make your apartment nearly inhabitable unless you spend some cash on soundproofing.
You could however look into some older smaller gear. S9's 841's 741's are all good in home miners if set up appropriately. Especially considering you don't have a plan to mine full time, you can save a lot on purchase price
Don't go crazy as a massive spike in consumption might end your free power with rent deal. Linking on mobile sucks so just google mining profitability calculator and you can compare earnings in different machines.
Thank you for your reply, the free energy i get in the employee building is linked to big industrial network that feeds a complete refinery; so i think we can see this free power as "infinite" (at least for few mining machines purposes).
How much money you think i can earn in one month with these machines??