Quite an undertaking for a first timer, but not something you can't do. I've done several kitchens over the years, a couple for myself, and a few for others. There is significantly more work that you might imagine, every box has to be made, and stored until installation. Every drawer, drawer front, and door has to be made and installed. Every drawer slide, and hinge must be installed, and drawers installed and adjusted. You kitchen will be out of service for the duration of the install, longer if you decide to demo, then build the cabinets for the space. Even with great planning you will likely be without a kitchen for several weeks, it isn't fun.
When it comes to the build it is all about square, and plumb.
I learned from a guy that did a lot of the trim and cabinets in houses that were built around here back in the '50's, so a lot of jobsite work. He was a great teacher, and if there was one thing he wanted you to get a grasp on, was the use of a story stick. It is your roadmap for a run of cabinets. It will have the length, depth, all the stiles, all of the rails, shelves, toe kick, and all of the partitions marked on the story stick, so it is an easy reference, for cutting, and as you are assembling the cabinets. And you can take the story sticks into your space and make sure it fits.
He would break the cabinets down into sections, as large as possible instead of building a lot of individual boxes like the store bought cabinets, just make sure you can get them into the space.
Square is crucial, measuring boxes corner to corner is a good way to insure you are square. Out of square affects everything, drawers will have issues, doors won't look right, it just cascades, so take the time to insure they are square. You will need a carpenters rule, this isn't a place to use a tape measure, accuracy is key.
Installation is fun too, no room is square or level, so a lot of work to get everything in there to look right.
And you know the effort involved in finishing...
Acquiring all of the materials, breaking them down, machining pieces and parts, assembling pieces and parts, it all takes time, way more than you anticipate. There will be waste, it will take time to develop a cut list(after you have made a drawing/plan) to keep the waste at a minimum. And there will likely be mis-cuts, so make sure you have a little extra materials. And don't forget your hardware, it will surprise you what the hardware will cost, I'm building some dressers for our closet right now, 12 drawers, slides are $13 a set for the ones I am using, you could easily have 30 or more drawers in a Kitchen...
So I would encourage you to really take a look at your cost, you will definitely get a better product, and have the pride of building it, but I think you will find the cost savings isn't going to be dramatic. And remember, you time really isn't free, it is time you could be doing something else.