I used to be part of a group of investigators (until they decided they wanted to be "stars" and try an get on tv - haven't happened yet, but I felt that some people were willing to let our credibility and purpose go down the drain if they could get famous, so decided to leave "untainted").
I can say that we had a few places that we really wanted to investigate, but couldn't gain access to.
One place was later visited by GHI (ghost hunters International) and it was pretty obviouse that the owners let them in because they could get some PR and possibly attract more tourists, so having something to "bargain" with might help - but I can also say that we've never paid our way in anywhere while I was part of the group.
Another place was an abandoned orphanage that was considered haunted and like your building it was in a terrible state, parts of it were in danger of collapsing - the company owning the land and buildings wouldn't let anyone in because it was too dangerous and frankly that's understandable, what if something did happen and they had let someone in? Every paranormal group in the small kingdom of Denmark have probably tried to gain access to the place so I imagine they are getting kind of fed up with it and last I heard there was talk of demolishing the place.
A third reason why you might/might not gain access is your professionalism and credibility. We had a few places that did let us in, who had previously turned down other groups, why? mainly because we focused on being professional, to leave everything as we found it, not disrespect their rules or wishes etc. That's back when credibility was important in the group - we all knew that in a field mainly made up of pseudo-science, faking just one piece of evidence or misbehaviour could ruin the group and any chance of gaining access to some of the places we wanted.
We made sure or homepage and stuff was very "see through" posting pictures and sound pieces with the main purpose of letting people judge for themselves whether or not it was paranormal - doing lots of private homes and outdoor areas (abandoned graveyards, battle sites, castle ruins etc.) before ever gaining access to some of the "cooler" places.
We finally gained entry to a smallish castle - once we could show that we had been to one castle (and that they linked to our site and only had good to say about our behaviour) more places started to let us in who wouldn't have let us in otherwise.
So basically you have to start somewhere - go to public areas, friends, families and gain some experience, once you can show that you aren't just a couple of tv-star wannabes it might be easier to gain access to different locations.
So don't keep bothering him - a no is a no at this point.
Don't act out or misbehave in places.
and don't fake stuff because that s*** will stick to your name and people will always have doubts in the future. So simply not worth it if you have in real interest in the field.
And be prepared for long, boring nights where nothing happens at all - because that's the reality of most investigations, it's certainly not like on the tv
That's probably the best advice I can give.