I'm not sure which stage of subdivision you got stuck at, but I'd love to have a look at your blend file if possible to get a better idea where you are at. However, if that's not possible, allow me to send you my blend file of the dome as I mentioned. You can feel free to use it in your project, and it might help you get a better idea where you went wrong on yours by studying the object.

Are you stuck at the end of the second video (which was really the first step in the process)? Or are you stuck on some part of the first video (the second phase of the process)? If you're stuck on the second video, then I think what may be happening is that you've added another subdivision modifier after you deleted the faces of the cube to get the dome shape? After you subdivide the cube to make it round, you need to apply that subdivision surface modifier, then go into edit mode and start deleting the faces as shown in the second video. Once that is done and you exit edit mode, do not apply another subdivision surface modifier. Just add a solidify modifier and adjust the thickness of that. Then apply that modifier as well.

Let me know if that is where you went wrong. If that's not helping, then I'd like to have a look at your .blend file. Let me know. If that's not possible, I'll send you my file.

______________________________________

My Store
My Free Models
My Video Tutorials
My CG Animations
Instagram: @luxxeon3d
Facebook: https://www.facebook.com/luxxeon