Best option is to speak to an accountant but in its most basic sense it will come down to turnover and profit.
Also related to that in the shopping centre where I have my business we have RMU (retail mobile units), basically 8x6 units with a little roof. I've seen several traders move from what appeared to be a long standing and successful rmu business into a bricks and mortar unit and get unstuck very quickly. Fixed cost overheads will mount up very quickly so look very very carefully.