First time travelling to Rome

Termini's baggage check works well for me.

It might be worth checking with the contact of the self catering apartment to see if they would be willing for you to drop off your luggage prior to check in. Also, we have been able to check in early if there is no one check out on the same day. It is worth asking.

I'm in the same situation. We're renting an apartment through VRBO. I emailed the owner, and he stated that we could drop off our luggage at the apartment when we arrive in the morning (we are having him arrange a car to take us to the apartment) and then return at the specified time in the pm. Have you tried that route already?

Me and my wife are in the same situation. We rented ours through Airbnb so I contacted the renter and they are willing to let us check in a little bit early. We are having to leave our bags at the train stations when we arrive in Florence and Venice later in the trip. I have done quite a bit of research and leaving baggage at the train stations seems pretty safe so i've heard.

We used a service called Bags Free in Rome. They were recommended by the agency from whom we rented our apartment. Their facility is about a block and a half from the train station, and they were very nice - they called a cab for us when we were ready to go to our apartment so we didn't have to worry about finding a stand. They also offer luggage delivery services.

At the risk of being repetitious, your first bet should be to contact the apartment owners.
We have done this several times - it is helpful that I try to be located centrally. Last year I had an experience in Madrid that was above and beyond - they kept our suitcase for us while we went for 2 weeks to Portugal to join a RS Tour!
But we have often just asked our B & Bs, Hotels, and apartments to do this for us for a few hours and never been denied.
Good luck and have a wonderful trip!

Thank you all for your responses. I have emailed the apartment rental place to see if we can leave our bags there, if not then I will check out your recommendations.

I too am a first timer heading to Rome and was told by my AirBnB renter to use BibboLuggagestorage.com

I won't bother repeating the good advice everyone else left especially since you're already contacting the apartment owner. What I will say is that on 2 ocassions now I've used a place called Stow Your Bags and have been really happy with the way they work. They have different locations all over Rome now so which metro stop is closest to you? They have a spot near the Vatican/St. Peter's and the A Line which is all automated and self service but still insured and surveilled like their other spots and you can still arrange airport transfers there with their intercom. Anyway, it's really cheap and is probably one of the easiest things I've ever done. The locker sizes are listed on their site too: http://www.stowyourbags.com To be honest I haven't used Termini station and wouldn't have a fair opinion, but this wasn't more expensive or anything like that and it might work out since it could leave you closer to your rental. Any response from your rental owner yet?

I will have a look into stow your bags as you suggested thanks for the link.
We can check in a little earlier, at noon instead of 2 so we'll only need to kill a couple of hours and think the best plan is using the bag drop by the property and the metro. I think they are near the same stop! I think we'll leave our stuff, grab a snack and get some nice pics of Saint Peters Square before checking in. Thanks for all the suggestions.
We'll use it again on our way out if we need to but are waiting to see if our property owner lets us check out late.

Darleen, stow at your apartment or the service Stewie is recommending as it's at least close to your accommodations. Termini would be fine too as you can hop the metro from there over to the Vatican area when done sightseeing.

I would hesitate to use the option recommended in the post just before Stewie's for multiple reasons.