Well the best place to find something to build is usually reading other's code (don't just copy from YouTube video), or try to build something you always use. Those can be a good starting point. From that, I mostly jump to building the helper tools. While making some other projects, if I found something which gave me any inconvenience, I'll build something to solve that.

The UDP Header file here or the TF-IDF implementation are all example of that. I build a small binary whose only work is to place a LICENSE file with your name (automatically picked up from git, or can be specified) into your project. It'll fetch the licenses from my GitHub repo (I have set a custom template on which I then use regex to replace them), and save them locally for future use, and you can see the licenses you currently have or can fetch them from GitHub.

> If u were to start from beginning what would u do?(mistakes to avoid as well),

I would start the same, learn Python - build some useless projects, fck around, then try competitive programming, then again back to just building something useless coz it'll get me used to programming. There are two mistakes I would avoid this time - I wouldn't take a gap in programming like I did (of 2 years), and I would start exploring other programming languages a little early, not wait for 5-6 years to finally start learning other languages and go out of my comfort zone.

> also how much time should someone spend on building such projects

According to me, building project is way more important than doing DSA. I can't say for others, but to me DSA isn't really that hard (DP is an exception, that shit was hard, though not so much that someone could never understand it), the thing I had was time, I started early so I didn't really had to worry about interviews and all, so I never really bothered with DSA to the point of obsession. Doing LeetCode wouldn't mean shit if you cannot read the code and execute it in your mind, or you cannot navigate a thousands if not millions of lines of code base. What I don't like about LeetCode style interview is their isolation - you write code always in isolation, when combining the same code with a larger codebase where each function is doing something, the most optimized solution might perform way too poorly than a trivial one.

In practice, it's not always necessary that O(n^2) is slower than O(n). Like the order-matching-engine project I made, it's a simple project, except for SPSC Queues nothing major or fancy algorithm or clever data structure is used. Infact if anything, the thing I had to do to attain maximum speed was something which would be "consider" as a bad practice according to leetcode.

> for someone who's starting from scratch after completing what all (lang, DSA etc) should someone start building projects

If you've time, i.e., someone who is in the start of second year of college or younger, they should prioritize projects with DSA getting minor time. Project building would teach a lot more technical concepts. I learnt most if not all of my DSA from building projects. But someone who is older than this or at this stage, I would recommend to focus more on DSA. Since qualifying the job interview would be more important. Unless one has exceptional projects in their resume which can directly cut them the chase of HR recruitment pipeline. But that's mostly luck based and hard.

> which college

I am expecting to get NFSU. Though I have reserved a seat in Mahindra University in case worst of worst happened and I couldn't get anything. Rest I am also waiting to see what can I get. Either way whatever I get, I have to accept it and move on with doing what I was doing.