I built one of these a couple of months ago:
https://www.ebay.co.uk/itm/274956579410
Depends what you want it for ... I just needed more storage - there's no windows in it and the headroom is a bit limited but pound for pound goood value. Seemed a bit flimsy but once it was up and all fastened together it's pretty sturdy, It does need two people to put it up ... a lot I did on my own but there are some bits that you do need another person. If you are any good at Lego then you will love the instructions - pictures and numbers - it took me a day to figure them out but once you get the hang of it not too bad. Needs flooring as well - comes with floor bearers but no floor.
Mind you ... just noticed - it's gone up in price dramatically - I only paid £629 - not such good value at £200 more !