I'm gonna say some things here that I think are right. I'm gonna tell you it's the way and you should always be skeptical of that. This world is full of people who want to tell you the right way and they're full of drek, so feel free to do it different if you see a better way.
You're going to take about a week to get ready for this, if you work hard and you're also lucky. Deckbuilding is really time consuming and costs a lot to get set up. This assumes you are already familiar with decking; get an Avatar and make do with that until you're ready for more. With that warning, here's the primer on how to build your beautiful Tier 12 cyberdeck.
1. Before you even start, you need your Computers and Computers B/R to be at the top of the biz (level 12). You can build a lesser deck at a lower tier, but you may as well start this with your dream project because it takes ages anyway and what you build will be temporary if it's not top-tier. Sell paydata and run errands 'til you're able to get the training you need.
2. Get your hands on the best gear in the biz, inferior gear is slower. You want a NVE-G250 rack mounted machine and a Hitachi RM-AX cooker if you can possibly get them. You will also need an unpacked microelectronics workshop for deck assembly, a bag of optical chips, and a bag of cyberdeck parts. Try to get around 50k worth of each. Better computers let you program faster, and better cookers let you burn ware faster.
3. Next up you want to slot a high quality programming suite on your computer. You ideally want this to be Rating 12, because it will speed up your work, and you have a lot of it ahead of you. Even an experienced decker will take some time to make this, so one good move might be to buy one. Or you could build one yourself, using your Program Design (Special) to DESIGN it and your Computers to PROGRAM it.
4. CREATE your deck. This part is fun. Get creative, you'll have it forever. Design it the way you want it to look. Give it at least one distinctive part of its name that isn't color coded, so you can access it easier.
5. CREATE, DESIGN, and PROGRAM an MPCP firmware program. This is the core piece that determines the level of the deck. You can LIST the ware on your computer to check your progress, this might take a lot of time so have a friend over and chat with them. You will then COOK the ware which sends it to your burner, where you can UNINSTALL it when it's done. You'll also need to CREATE an MPCP part, which you're going to combine with the firmware and BUILD into the deck. Make sure it's as high tier as you can manage - here we're aiming for twelve. Here you will start to need optical chips and cyberdeck parts, so have them lying around in a place with your microelectronics workshop deployed.
6. CREATE and BUILD an I/O part, a matrix interface, a storage memory, and an active memory into your deck. These cost a lot of optical chips.
7. CREATE, DESIGN, and PROGRAM a bod chip, a sensor chip, and a hot ASIST. You'll want to combine each of these with the corresponding part you CREATE.
8. Your deck will now start up, congrats! It's not done.
9. You want to CREATE, DESIGN, and PROGRAM at the very least hardening (this is a pain in the ass to make and takes ages but it is necessary to face black IC), a masking chip, and the standard suite of programs you use as a decker already. Sleaze helps IC not detect you. Deception helps you login to places. Evaluate finds paydata. Defuse and Disarm will clear it of hazards. Read/Write lets you download it with ease. Those are the most important ones.
10. Optionally you may also put in an ICCM, a RAS, a reality filter, a reaction enhancer 3 and whatever other parts you think would be cool. They're not necessary but they're gonna make you better out there. Many of these things will give you an edge and compensate for abilities you still need to practice.
Okay, I'm done. Sunny's is more detailed so definitely read that too, but you wanted the cliffnotes, didn't you?