I think it really depends on how you make it. Layering throughout the old world was standard...even in hot places like Spain and Italy. For example, in warm moist climates, you often see more linen used in the undergarments like shirts and shifts. The increased volume has two effects, it allows more airspace under the outer layers to maintain a cooler interior as well as increases the amount of fabric against the skin to absorb perspiration. In early America, it is interesting to see that English colonists made a significant effort to modify their clothing for the heat and humidity when they came to Virginia. In contrast, there is little evidence that Spaniards changed anything when they came to Florida during the same period. Personally, I have lived in the AZ desert as well as here in Virginia and I can speak from experience, the humidity changes everything. In AZ I was able to wear quite normal layering for Spanish clothing of the early 1600s but in Virginia those same outfits are much more uncomfortable. Once I sweat through a shirt though, as long as I keep moving, a breeze comes through the outer wool layers cools me down inside the clothing. The worst fabrics to wear in humid, hot weather are silk and cotton. Wool, especially if it is plushy but porous is best...with the linen beneath, it acts a little bit like an air conditioner. The linen wicks the moisture from the body and the wool, being a protein fiber, doesn't want to hold onto the moisture. If the fabric is porous enough, the air just evaporates the sweat. I have even had a couple of occasions where I've gotten cold wearing a wool suit over linens in hot weather. Rare, but it has happened. It is counterintuitive to our modern way of thinking about comfort but It is so much worse to remove layers and expose more of your skin to the sun and ambient temperature. I have been known to put another layer on when it is too hot, just to put more distance between my body and the local weather. Records show that temperatures on the rise...but also records can show that similar temperatures were present in history -- so I search for history's answers to climate and dress. Knowing what they did in the past is how I choose my solutions for today. If I think like a modern person, I tend to get it all wrong.

But your shoulder are double, I think I will do double and ruffle neck and Sam blouse.

I'm sorry you're having issues following the video. If you're new to what I do, I might recommend watching some of the other tutorials for more clarity. All my patterns are given as proportions of different measurements from your own body. These divisions are based on the Bara system of measure and cutting which comes from an earlier century. It is how I deliver all of my patterns because people can calculate the exact measurements for their bodies without having to do too much customizing. The measurement of the slit IS in fact given at 2:54, if you pause the video and look at the diagram, you will see that it is given as a proportion of the chest measure. 1/48 of the chest times 10. The center front of the shirt is along the fold, which is the upper edge of the diagram. All of the measurements are given as proportions based on the chest for the widths and the upper body depths. The overall lengths are given as proportions of the height of the individual, making the pattern scalable for whatever size you're trying to make.