If you are making one with Raspberry Pi, you will typically need a Raspberry Pi 4 with 4GB or 8GB or ram, a 1TB or larger (2TB preferred) external SSD, a 32 GB micro SD card, power supply, case. Follow guides for either Raspibolt.org (my favorite), Raspiblitz.org or if you want a simpler web browser oriented interface and point and click install . MyNodeBTC.com

But if you don't mind a machine with a larger form factor and a slightly higher budgetI'd recommend getting a refurbished Dell Optiplex (~200 to ~300) and putting a 2TB or larger SSD in that. It will perform much faster for synching validating blockchain. Setup process is similar as raspberry pi for the above but in the case of Raspibolt you'll need to use x86_64 architecture vs aarch or arm64 for the software you choose to install. If going through easy route with MyNodeBTC you'll need to choose the PC image instead of the one for raspberry pi.