good evening. I live in Florida and im having a hard time understanding all the legal-ease when it comes to what is allowed up there. My mother still lives on the north shore and she's wanting me to build her an AR after she visited me and shot a bunch of mine. Can someone point me in the right direction in regards to what EXACTLY needs to be on it for compliance?

from what I think I've gathered so far is that it has to be a p/w muzzle break (no flash hider), fixed stock, and a fixed magazine? anything in regards to trigger? she told me her handgun has to have a 10+ pound trigger pull weight, is this true?

I just responded to your DM about the AR.

Be aware that you can't possess a gun in MA (i.e. bring it to her) without a MA NR LTC. If you get caught with it, it is a felony and PP federally as well.

No her handgun does not have to have 10+# trigger. There are certain restrictions on what a MA dealer is supposed to sell, but the buyer can modify and own any handgun that isn't a so-called "assault weapon". My carry gun has a 4.5# trigger pull, done by a gunsmith for the first owner of the gun. I had a master gunsmith do 5# triggers on a number of my handguns.

if they can own any handgun, why are there hand guns listed as MA compliant?

The MA GCA of 1998 was basically an anti-gun dealer law. It intentionally shrunk the number of MA dealers very significantly and put a lot of other restrictions on what they could transfer. It was tagged as "consumer protection" from dangerous products, so testing is required and a lot of other things that also makes it unattractive to mfrs. So many mfrs kissed off MA and don't submit their products for approval in MA.

As a former resident of the Commonwealth my recommendation is: don’t. For an AR on MA you’ll end up paying silly money for some old junk.
It won’t be cheap either way. So if she wants a rifle of that sort I highly recommend the 16” X95. Perfectly legal, available at several places and a top notch brand new 223/556 rifle that’s good for anything from fun at the range to home defense to the zombie apocalypse.
Pre 1994 mags are available, legal and fit.
If you decide to go that route make a few phone calls to the stores on the South Shore. Some dealers may only carry the 18” version - not understanding the legal situation. The 16” is Mass compliant and they can obtain it directly from IWI in PA if they don’t have it in stock.

They trick is that you can technically “own” any handgun, but you can only sell what’s on the approved list. So you can technically own a Glock - but you can’t buy it anywhere. And then there is the ten round mag limit - which further reduces the models you can even own (for all practical purposes).
Best options in MA are Sig (you can drive up to the Sig factory store in NH and buy whatever is MA complaint and have it transferred - highly recommend it for the experience. They let you test things also). Walther is available (not all models). All things Springfield and Smith & Wesson for those who like that sort of thing). Many others. You can look at the list on the state’s website. Yes, all this is nauseating.

Both bolded statements are untrue. The law is a dealer restriction only. Private sales have no such restriction. Also, there is a legal way around the dealer restriction that is practiced all the time.

Yes. Not sure how practical that information is for the OP. The MA situation is complicated. Some of it is rather grey and who wants to be the one testing the stupid laws in court? I personally never bought and never would buy from a private seller in MA. I know people in MA who bought used Glocks. Most dealers will not sell them. And I don’t think you want to be in a situation where you use one of those in a self defense situation in that silly state. Chance are they will go after you for having carried a gun that was deemed “unsafe”.

The whole thing is stupid but there a plenty of good options when going to one of the reputable dealers. Given who is now governor and with the latest ATF raid in MA I would recommend keeping things simple. Make sure to have an unrestricted LTC from the respective town (most are actually easy, a few nasty ones - OP’s mom is on the North Shore so it should be ok).
When we were still up there we bought a few Sigs and Walthers. IWI for a modern rifle without being hassled potentially. YMMV