Hello.
I’m trying to become at least “decent” in my building skills. Just trying to figure out exactly what I should build. A friend of mine suggest a metro system, but I know I will easily become overwhelmed from trying to do that.
Decided to come here and see if you guys had any ideas what I should build as a beginner? Any suggestion is much appreciated.
Build something small, such as a chair or a table.
Build anything. You could take a look at your surroundings a build the first thing you see and/or create what you most enjoy i.e. Sci-fi etc.
you can first build the out side of a house
then build that bigger and build a inside
you can build a very low detail car
or a kamp fire
i’ve a game about it, i dont spend hours on modeling
Build whatever you feel like, a house, a town… there is endless of ideas.
If you’re using Studio to create builds, I suggest making a small house or if you were using Blender maybe make a small low poly map.
Note: This is about blender since most roblox 3d modeling takes place here, if you are just using studio you can ignore this.
You should model what you feel comfortable with and enjoy like hard surface (guns or like a metro, human made) or sculpting (animals or humans, life like stuff). If you don’t have any prior experience at all you should watch a tutorial, heres one about a chair Blender Beginner Modelling Tutorial - Part 1 - YouTube.
Getting into the building world is very exciting and can be very overwhelming at the same time, it’s good to know your comfort zones especially when you’re just starting out. I highly suggest that you watch youtube tutorials and build the things that they are showing, this can help improve your building skills and make you more of an accurate and well-developed builder.
Another form of practice I like to use is just google images or any image. I love building the things I see. Just search up small cool places online and look at some images, try and replicate those images into your builds. You can even add your own detail and spice it up a bit by letting your imagination take hold and adding cool things.
Another thing is you can build things you are familiar with, like places you’ve been or places you love to go. Or maybe a relative’s house and such. Just small things, know your limits. Always make sure you are enjoying what you are building, if you are stressing out way too much and just feeling hopeless, maybe that project is not the right one for you. Since you are just practicing always make sure to have fun while doing it.
Good luck! 
You should build things that you enjoy making, as that’s a way you will gather a bunch of beginner build ideas to start with you could even write them on a piece of paper. Viewing made topics includes a bunch of information and overall ‘building ideas’.
Consider starting small and then you will slowly increase your skills start with a 'house - table/chair, vehicles, weapons. Use reference images online to get some ideas on what to make, looking for ideas can come in many types of ways I won’t go further since that are dozen threads already;
You may want to use the search bar and see if your question hasn’t been already discussed in previous topics.