2 things come to mind . No need for a 12' ceiling ever and fake beams always look fake. IMO 10' is the max ceiling height and it will save many $$$$$ on heating and cooling over the life of the home . As an aside I always ask clients what they plan to display on a ton of shelving . Most have a min. of special things that need display . TV over the FP worst choice for proper view height..If at all possible this is the time to ake sure you get it right.

For beams to look appropriate, whether false or structural, they should be a size that looks as if they are actually supporting the ceiling and materials above. The sticks in the sample picture look woefully undersized to my eye. Using a rule of thumb of span/15, you'd need 16" deep beams. Maybe you could cheat a little off that and still look good.

I'm skeptical of the knot less pine. One other poster had false beams installed and the GC had used individual boards pieced together to wrap a 2x framework and the seams made it evident it wasn't a beam. 20 ft. long clear pine in the size you need isn't readily available.

Thank you Seabornman! Yes the wood would need to have a seam due to length of beams available. Builder definitely uses wood beams, not wrapped. So I’m interpreting you think 4 12” beams are not too large for the space?

Love my 12 ft ceilings and large built-in shelves! I designed my house to display art and decor collected throughout my life!

Our builder used Radiata Pine to do our boxed beams. Sure they aren't truly authentic, but I just like the look and detail they add to a plain tall ceiling. Yes, ideally I would have used real reclaimed lumber, but my build was during covid and I didn't have the time or patience to try to source those. There are also some very realistic rustic ones available that are made out of some composite material. I think mine are around 12" wide and 8" tall.

We are in FL so we didn't want a fireplace, but I would not have placed a TV over it if we had done one, unless it was a low and long modern electric fireplace.

12" would be the minimum I think. Make sure they're wide enough. Can you get who we created the rendering to show them that size?

Thank you Patricia! The ceiling is already framed and electrical ran. I was going to design the builtins to this picture. We’re used to TV over fireplace and don’t mind because we sit back about 11-12 feet. Were concerned that a 65” TV off to one side will look off balance with other side. However maybe we aren’t understanding a thought you have. Any input or pics are welcome! Thoughts about the beam size ?

A typical post and beam structure would be built like this. With a ceiling surface applied to the bottom of the smaller members, much of the large beams will be hidden.

Where a wall runs under a beam, you would only see part of the beam

And just for looks, I might consider an infill board running between the beams.

PPF got it right. The tops of purlins would be level with the tops of the structural beams so only about half of thse beams would be visible. A 12 ft ceiling height suggests the house style is not rustic so there would be matching trim rather than beams at all of the walls.

The beams shown below are abour 4x6.

You should be working with a good designer or finish carpenter.

Looks nice PPF. Instead of structural post and beam, the framing of ceiling is complete. We came on the scene after framing was complete. The builder is adding clear pine wood beams as a decorative. 12” wide beams one on each wall and two flanking the fireplace. I thought 12” wide seemed like a lot but others posted 12” would be ok and could be bigger taking span/15 as rule of thumb. Thoughts?

I thought 12” wide seemed like a lot but others posted 12”

Others were suggesting 12" tall, not 12" wide. Beams are typically taller than they are wide, but not always.