Loft grows are a high risk op.
A continual grow cycle in there is obviously even higher risk.
You could grow 6 months out of the year in 2 month installments if you went with the lowryder. 9 weeks to finish from seed, you could maybe SOG them. Either way you could get alot in smaller spacer, and could be looking at nice yields if the conditions are perfect.
The only downside to LR would be the 18/6 light cycle. If you were to do other plants though, you're looking at an 18/6 cycle for not much less than the same amount of time anyway.
9 weeks growing, 7 weeks off.

Besides that, how often do you see helicopters fly over your house? Never mind a police helicopter? Just don't draw attention to your property at all, so the police will have no interest. (E.g don't deal from it.)

EDIT* just a tip, it's debatable which is better, white walls or mylar.
also pay only in cash in the grow shop.