well, the No.1 rule for a good grow room is that its gotta be cleaned properly, like, disinfected, scrubbed, hoovered, disinfected again, scrubbed again and washed.... that way your plant wont get any diseases... so its probably best to either empty your shed completely, or scrap the whole shed idea...

as for nosy neighbours smelling it, buy/make a carbon filter, and make the shed airtight..

good luck...