I find a good way to go about this is always check the current version of PS or LR on the adobe site and see what the OS / Hardware recommendations are set to. once you have this information saved, take it to a computer store that manually builds computers or check one of the department stores for something with double the recommendations if you can afford it, this way you should be good for a while as more iterations of the software comes out for a few years.
IE: if the recommendations say 8GB ram, double it to 16GB ram. if the processor requires an i5 intel, get the next version up or higher. if its graphics card x, get the newer version of y.
most computer stores will be able to sort out with what you are looking to do and should assist with you getting the correct setup.
when ever you are looking to buy a computer, never just consider just one piece of software but everything you plan to do with it. if its music, home videos, photography, games, coding, virtual machines, etc, that you can meet all requirements without breaking the bank.
Says any intel or amd 64 bit processor, that would be the lowest i5 you can get, where as you get an i7 4 core or 6 core processor, you will be a head of the game and have more processing power. the ram says 8GB so i say 16GB ram. and a graphics card with 1GB of ram so get one with 2GB of ram. all the other parts will fall into place like how much space you need most people are running TB drives with SSDs.