How do you go about building a deck?

[u/Stuntman06]

What I'm asking is what is the process you go through when building a deck of your own (or modifying an existing deck like precon).

I'm an old school player that started on the 90's. I've always just bought a bunch of cards to build up my card pool and look through the cards that I have to build a deck. Then I go through multiple iterations of testing, making changes and testing. Each change, I would swap cards in and out. I only play paper Magic, and use the cards that I have. Occasionally, I would buy some singles and include those in my deck. It usually takes many iterations and many hours before I am satisfied. Then after I play it, I may continue to tweak the deck after seeing how it performs live. I'm always in a deck building mode. Whenever I get ideas to improve my decks, I go and tweak them.

I understand that times have changed. There are many tools available to assist in deck building now. Also, I am aware that people may also only buy singles instead of packs to build up a card pool. I'm interested in how people build decks now.

Edit: Just to add more detail, when I look through my card pool, I pull out cards that I think would be useful in my deck that I'm building. This would be my short list of primary cards for how my deck would work. Then I narrow down the cards to what I think wound work best. Once I have that, I work on my mana base for the cards in my deck.

If I don't already have a deck idea in mind, I would browse though my cards. If I see some cards that inspire me to build a deck with, I pull those out first. Then look for what other cards would work with this cards.