The one thing I realized right away was all the stuff you take for granted on complete bikes that add up super quick. Oh you got some sweet disc brakes? You need brake lines, and brake fluid and have to know to set them up and bleed the lines, and you need brake levers. Oh, nice wheel set, you need tires as well, and you have to get the wheels trued before you put them on. You need a crank set, and pedals, and a chain and handlebars and a proper stem and grips and the list just goes on and on.
It took me about three months to get all the parts together. I kept everything in the box at the shop, in the basement. Once I got everything together, myself and two mechanics who love building bikes, sat around the shop putting it all together which took quite a while.
It was a pretty big wakeup call that yes, you can build a bike from scratch, but you also need a huge amount of knowledge and patience to put it all together. Even after I had put my bike together, it took several attempts to get the disc brakes dialed in which I've never had to deal with on a floor model. Same thing with the drivetrain and getting both derailleurs dialed in.