When you make a short sleeve t-shirt from scratch (using t-shirt pattern), can you use a pattern with the sleeves attached?

Greg, an ordinary T-shirt has separate sleeves that are attached after the shoulders are stitched together at the front and back. Then the side seam, from the edge of the sleeve down to the underarm and on down the sides, is sewn.

If you're reluctant to cut and sew a separate sleeve piece, you probably want to seek patterns that have what's called a dropped-shoulder sleeve. Here's two examples: https://mccall.com/b6768 and https://mccall.com/b6774

There's no sleeve piece, just the shoulders sticking out beyond the person's actual shoulder. It could go on far enough to create a long sleeve, in a knit fabric anyway. In a woven, it would wrinkle and fold too much.

Another option is the raglan sleeve, which is a separate sleeve piece but easily attached to the shirt with a straight seam. Baseball jerseys are usually raglan sleeved. Here's one: https://images.app.goo.gl/SYv68wAKkBinZ1Pv9