As my current PC, while probably still being on the upper end, is already 6 years old and I can currently afford it I wanted to build a new one.
The problem is that my knowledge about hardware has gotten quite a bit outdated (I didn't have the money to upgrade so I didn't bother looking into it), so I'd welcome any tipps or recommendations.

I would like to use the following:

CPU: Ryzen 9 3900x (as the 3950x seems to be way too expensive)
GPU: RTX 2080 Ti (not sure which one, I usually buy MSI ones but I don't know if the quality of their products changed over the last few years)
RAM: 64GB
SSD: 2x 1TB (probably from Samsung as I never had any problems with those)
HDD: 2x 4TB
Case: No idea
Mainboard: Also no idea.

If you don't have specific requirements for cases, I'd start with the Fractal Design Define series and see if there's one that suits you. These are pretty decent cases overall. https://www.fractal-design.com/products/cases/define/

You'll also need to figure out a CPU cooler, which might affect your case selection.

(I have a Ryzen 1800X on Asus C6H with Noctua NH-D15 in Define R5)

You probably want the fastest possible RAM for Ryzen, but you might not be able to find it in enough capacity for 64GB.

(I don't know how the memory controller in current Ryzens are but the one I have is very picky, and populating only two slots with single rank RAM would make for ideal performance)

Two tips:

1. Don't skimp on the motherboard.
2. Don't skimp on your PSU.

I know "future-proofing" is a meme, but spending a few bucks on a good mobo that has a solid window will make it much easier to simply upgrade processors when something newer/shinier comes out.

PSU is just common sense, especially if you're planning on slapping a 2080Ti in there, not to mention, a good case/PSU/mobo combo now, will save you some cash in the future when you just want to swap out CPU/GPUs.

I just built a new rig right before Christmas, and the main thing I spent on was the mobo/PSU.

I've just built a 3700x, so not quite the monster you're trying for but here are a few things to consider:

- Work out the Motherboard before settling on RAM and HDDs.
- Check the compatibility of RAM and buy RAM that is on the tested list - this might cost more money, but it is more likely to work. I'd personally go for 32GB rather than 64GB (I actually only got 16GB and it's currently fine) - 64GB is nice, but might be a nightmare to find sticks for (and on some motherboards, they're very finnicky about having 4 sticks - they play nicer with 2)
- You'll want a high end motherboard; I'm assuming at least one of your SSDs will be a NVME M2 drive - if both are, you'll want to go for a 570 motherboard rather than a 450 or 470 for the extra channels. If you go for B450, on many designs, putting in a NVME drive in will disable a couple of your SATA ports. So, if you have a DVD drive as well, you might run short.
- A second NVME drive in a B450 is unlikely to run at full speed and will disable a number of your PCI-e slots (although most people only use one PCI-e slot for a video card as people generally don't use discrete sound and network cards anymore - although a consideration if you don't have onboard wifi)
- Case - just make sure it has good airflow
- Graphics cards - my GTX 660 was a MSI, and my 2070 Super is also a MSI - I've had no issues.

Hope this helps!

I'll decide on the PSU after knowing the whole build (I still have the 1000W one from my current PC can I still use it or did the ports change?).

As for the Mainboard, I'm just completely lost there. Like I said I didn't bother about it for almost 6 years so I have no idea what's currently important, what problems some models might have and so on.

Is there one you could recommend? The ASUS ROG STRIX X470-F GAMING and the X570 version both look decent but I don't know if there are better ones out there or if the X570 version is relly worth the higher price (I plan to use the 2 SSDs via SATA).

You are so right there, and it cannot be stressed often enough not to compromise when it comes to main components (which you could define as heart and lungs of the PC), and PSU is certainly one of those. Given the specs of that intended build, that's gonna be a power hungry beast and you do NOT want to go cheap on the PSU. Personally speaking, I stick with Seasonic and their 10 years warranty on many of their models. You get what you pay for and so far, that's one investment (PSU) I haven't regretted. Not to say it can never go wrong, but I'd rather a more expensive PSU that's gonna go down on its own than a cheap one that's gonna fry other components along with it.

Thanks.
I will use the SSDs via SATA for cost reasons (I know it sounds wierd considering what I plan to build, but I had to cut it somewhere).

What about the 4x16GB which are on the tested list?

Then I'll stick with MSI for the Graphics card.

I wouldn't buy the current line of graphics cards, instead wait for the new 7nm line of nVidia graphics cards which supposedly will be available later this year.

The SATA SSD's may be a bottleneck on your planed system, depending on what you will do with it. NVME are not much more expensive than SATA. Consumer grade flash tend to slow a little after some time, if you plan to stick with this build for some time, may be worthwhile to invest a little more on NVME.

Keep in mind that Windows 10 (if you plan to use it) abuses of storage drives and will do much more on the future.

And yes, it do sound weird to go for a 1200$ GPU and save 30$ on faster storage :P

Unfortunately I have to use W10, it's a gaming system after all and as much as I like Linux it still can't completely replace Windows.

As for saving money, I'm already at the limit of my budget for this if I want to buy it before C2077 (I can only save up to 3100€ until April) and using the SSDs via SATA not just saves at the SSDs but might also allow me to save another 100€ at the mainboard and additional 100€ because I can use the SSD from my current PC. Don't the Ti cards usually get released even later which would mean I'd just regret buying a normal one at a higher than neccesary price with potential software issues. At the point of its relase I might also wait for the generation after that....

Agreed with this. The price/power ratio of 2080ti is horrendous.

This. My original build included one until I looked at the price point and realized that if I downgraded to a 2070 Super, I could upgrade a lot of the rest of my build, which I did. I mean, a 2070 Super could also fall into the perf/price point argument, but it was this or a 5700 XT Red Devil model which was still in the ball park, but eh.

Don't try to save money on the PSU or motherboard.

It's been a few years since I built my machine, but pcpartpicker was a really helpful site when I was planning it out. Lots of good advice/discussion on their forums and nice tools to put a build together then post for feedback. I assume they still have a good community to advise. Haven't been back there lately.

I do not want to suggest very specific parts if the building time is not imminent as prices and availability change and new parts arrive but:

Why 2 x 1TB SSD?! Why not something like this (excellent for the money): https://www.caseking.de/adata-xpg-sx8200-pro-series-nvme-ssd-pcie-3.0-m.2-typ-2280-2-tb-ssad-053.html?

SATA based SSDs are like a handful of €uros more than the M.2 NVMe, not worth saving so little for a system drive.

Why two hard disks á 4TB instead of one that is 8TB? Though I can think of reasons for this.

With current RAM prices I think rich people should go for at least 32GB. Check the motherboards and processor (specifically its memory controller) whether to pick two or four modules or the other way around, pick parts that maximise memory speed and bandwidth. That is usually either double sided RAM modules or four modules.

The cheapest motherboards are not really suitable for the more expensive processors. I doubt putting a Ryzen 3900X into my X570 is a terrific idea, which was the cheapest I could find that week.

Nvidia's RTX 2080 Super is the most expensive graphics card with a decent performance to price ratio. This is a fact that may change quickly of course.