I think what I am going to do is I will send my friend to a hotel so I can stay at his apartment while I am there...just to respect the rules of the country and not to breach the law!
I hope they will not deny my visa application just because I am from Slovak Republic and not married so they might think I want to stay in Qatar. That is why I thought I will provide a confirmation letter from my employer and the copy of my payslip too just to give them enough proof that I will be coming back to the UK.