not to be harsh, and i don't know where you are, so you may have done the right thing for you, but by and large, in most western countries, this is the worst possible advice. NEVER invite a cop in, regardless of the line of shit they feed you. a warrant is specific (again, generally speaking and this may not be true in some countries) - it doesn't grant them cart blanche to toss an entire house, and they can only collect evidence that pertains to the supposed crime. once you invite them in though, they're good to go and you've got significantly less of a leg to stand on. generally speaking, everywhere i've ever been, cops do not negotiate, they interrogate. your job is to let them do theirs, by shutting the fuck up and not giving an inch more than you legally have to.
anyone growing where it's illegal should know as much about the law as they do about nutes, lst, auto/photo, etc. know your rights and your chances in court go up tremendously. had a buddy who was raided and a public defender was able to get him off because the cops exceeded their warrant. had he admitted to anything, invited them in or possibly even said anything except 'i will only speak with my representation present' he'd probably have done time (this wasn't a one plant operation).
anyway, good luck. get as good a lawyer as you can.