You posted in the plumbing rather than HVAC... but here's my $.02:

First you recognize this is really odd. You have hit on the major issues:

1. Sounds like you have an oversized AC unit for the bedroom. That would tend to reduce the temperature without reducing the humidity level in the cooling season.

2. You have tested for other sources of moisture including from the floor (are you on a slab or on crawlspace / basement?)

3. You have tested for water in the walls and have a new roof.

Now what about the following:

1. have you ruled out plumbing leaks?

2. have you ruled out a clogged condensation line on the A/C unit that allows water to back up into the room somehow?

3. was the master bedroom an addition or significant remodel?

4. There isn't a humidifier on the master bedroom furnace by chance is there?

You need to know that you have an accurate way of measuring humidity such as a digital hygrometer.

If you are using accurate test equipment and are getting a significant change in humidity from one room to the next while the AC is off for several days, you need to find out why before you do anything else.

Thanks for your input we are on concrete slab here in Florida I can feel the humidity so the meters are irrelevant , but this is just a little meter you get on Amazon . we have checked the HVAC lines. Can It be something as simple as our bathroom does not have an exhaust fan? But the mildew smell I smell as soon as I walk in the room which is nowhere near the bathroom ! I do believe the ground outside around my room is damp but I cannot start busting up the foundation!

No the meter isn't irrelevant - it's everything. You don't want to be chasing ghosts or what you "feel".

If you have a trusted meter and it's showing twice the humidity make a couple of tests a day. Try to make valid comparisons (not after a shower or after you have been sleeping in the room with the door closed all night).

If you consistently have reliable readings that are significantly different you must find the source of the moisture.

thanks. ill do that!

The mildew smell is a symptom - not the source of the problem. Odors travel, and I'm not negating how you perceive things, but chasing smells and how much humidity you feel isn't going to get you to the source of the problem.

Certainly having a bathroom with no ventilation will increase the humidity level of the surrounding room from the showers and such. You can rule that out as a cause by showering in a different bathroom as you monitor and record humidity levels with your meter in your bedroom vs the rest of the house.

Again though, if you are consistently seeing a very high difference in measured humidity levels between your bedroom and the rest of the house you must find the source. Ruling out things like the bathroom will save you a lot of money and frustration.

You didn't say if your bedroom was an addition or major remodel at some point in the home's history.

thats a great idea. thanks. this house was custom built in 1991 (i have seen it go up stage by stage, its on concrete slab) which in and of itself , cant be a good idea. with damp ground in florida!!

Typically a house built on a slab will use a plastic vapor barrier under the slab to prevent moisture from being wicked up into the concrete. That was part of the reason for the question about the possible remodel.

If your house was built all at the same time it's likely they would done everything the same throughout the house. If your master bedroom had been an addition, I would be more likely to question the construction details. What I'm hearing is that it was all built at the same time and recently. I'm sure that they used a vapor barrier.

im sure they did, but why do we assume that moisture barriers are effective? dont they degrade over time? seems like a ridiculous practice. and by trapping the moisture over the slab arent we still producing mold under the vapor barrier? houses here should be build on stilts!!! for air to ciruclate. our ground is much to wet here!

Did you look at the link?

The plastic goes directly under the concrete to prevent water from wicking up into the concrete. It's very effective and lasts a long time as long as it's properly installed (much of the article was about proper placement of the plastic --next to the concrete without a layer of gravel or sand). They specifically mention Florida.

Do you have any evidence of the concrete floor being damp such as seepage or loose tiles?

I do not have loose tiles I have a "sixth sense" that the tile floor feels damp in areas, I'm going to try removing the hvac unit and monitoring the bathroom humidity