Hey! I have quite a few tips for you myself; hopefully these help out a bit!
So, first off, I’d start off with smaller builds and projects. Get to know how unions, and negating, as well as building certain difficult parts in general works, so you know how these work in the future. You can always use reference pictures or models for this; similar to art and how when drawing, artists use references at times to make something. Building takes time for most to learn and get truly good at; take your time and learn at your own pace. This will take time but it’s truly worth it, you’ll get better and better, and eventually, you’ll be a great builder before you know it with work and practice.
Practice makes perfect and is key when building. Never forget this and always use this advice; time is key, don’t rush a build, even when you have time constraints. It’s better to have a great build that took lots of time than have a not-so-good build that was rushed completely. YouTube tutorials can help but will not help you master building unless you take the time to learn yourself. Take free models from the toolbox. Take them apart and see how they were made with the unions and all that is in them, then try to recreate it yourself, and if you get confused on how to do something ask here on the Developer Forums. It may not be too good, but that’s okay! You’re learning. A very famous quote that I love, along with many others: “Your first game will be awful. But you can’t make your 50th without making your first. So get over it and make it.”
This is how true success is made. Take your time and learn. Your first few projects may be horrible and that’s normal. You’re doing the best thing you can do, and learning. Look for feedback on builds in the Developer Forums, and you can learn even more, through suggestions of others who have lots of experience in building. Use their tips, and learn from them. Keep using and noting what you’ve learned in the future. This is how I learned. When I first joined the Developer Forums, I looked at feedback people had received on various builds, and then tried recreating free models from the toolbox, not doing the biggest models right away, and doing smaller things, such as a door, then learning how those were made, and attempting to remake them on my own.
Don’t be afraid to use reference images either. Almost all developers use these and they will allow your creativity and skills to be put to the test. Try making some changes from the original reference image. Now you’ve got yourself a unique build inspired by another building, in real life or in a game. Then keep trying this. Try combining multiple builds, to make a town, or a city, or restaurant; anything that combines your work into one game. Watch how others make something such as a table and learn modeling that way. Once you have enough builds, and enough good models you have made, not only have you learned to build, but you could possibly even attempt a larger challenge, like a showcase game or vibe game yourself. Let your creativity run wild when you build. Once you feel confident enough, attempt to make your own unique builds, like a house, or a restaurant, maybe a cafe. These will pay off majorly in the long run and can bring you success once your skills are enough to undertake these things. It will not only allow your creativity to run wild, it will allow you to put skills you have learned to the test and get better at what you are doing. There is always room to learn something, no matter how well you know it or how much you have worked on it.
Take your time to learn all this. Use the tips I have above. Put your skills to the test once you feel comfortable. Use tutorials, use reference images. It’ll be difficult but it will pay off. Keep this in mind and always do your best work, and you’ll get there. Your first builds are gonna be bad. Don’t lose motivation because of that, use it as motivation to work harder and get better over time. It will, and I mean it, pay off eventually.
All in all, there are so many ways you can learn, and I wish you the absolute best of luck learning how to build. Hopefully this helped out a bit, I got a bit carried away typing this.