I had a bunch of spare parts from computers I had parted out in the past, and I figured I could build a computer for my girlfriend with them so she could play games her laptop wasn't able to run.
The motherboard, GPU, RAM, and case were all parts I already had on hand, and I just had to buy the CPU, SSD, and power supply. I also had a spare monitor I gave her and I bought a RGB keyboard and mouse for her.
It took me about 2 months to get all the parts together since I was doing research for what the best parts/value were for the build. I ended up giving it to her as a Christmas present.