I'd say totally scrap the HDD for a 256gb SSD. Large HDDs are only useful for people who really don't want to delete stuff(like me, I have TB's full of useless stuff that I just refuse to delete). And also if you do need the extra space, you can always put in a new HDD down the road, where you will probably get better GB/$. External HDDs are so cheap as well that if you really need the storage you can get one of these and rip out the HDD from it's enclosure

Don't forget about the simpler aspects of gaming on a PC such as how loud it will be. For me, I love a silent computer and less flashy(hate LED lights)

And while everyone is advising on upgrading the GPU, I'd just inform that changing the GPU in computers is extremely easy. If your GPU is too weak after a couple of years you can always sell it and upgrade.

Personally I am also planning on a PC build but my friend is getting me a great discount so most of the choice is out of my hands. I plan to just take my current ancient GPU and use it up until Christmas and will upgrade then.

Hope this helps.

thx for the advices, I'm still looking to make the right choices.

As an ex PC gamer, I would recommend buying a console and buying a crap ton of games for it. That will get you farther than the PC even with steam sales ect. But that's just my experiences with it. You can buy any one of the 3 systems and get 30 games with an average cost of $20 per without any of the worries of configuring your game to work for roughly the same price as what you are looking at. Of course if you want FO4 it's gotta be the X1 or PS4, but that still stands either way.

I got a ps4, ps3, x360, wii already

Then just buy all the games you want with all that money. IMO, they will serve you better. 

I personally found even after spending a good amount of coin on a computer there always seems to be parts you will find that you want to upgrade. It almost becomes an obsession, at least it did for me to a point. I never went high end or anything like that because I couldn't bring myself to purchase a GPU for the better part of what you are paying for your whole rig. But after a couple years the mid range would show that they were mid range and it was very easy to find an excuse to upgrade. Sure it's only a couple hundred bucks here and there, but it adds up. Account for the initial cost and the little extras that go into it, time and time again, and I spent far more than all the consoles combined in a generation and missed out on many of the great exclusives during that time. I found I would almost needlessly upgrade just for a few games that I mostly played to look better, or their best. Always great right when you switch the GPU or notice the speed of loading with new RAM and/or CPU, but it wears off quickly. 

Like I said, just my experiences with it. I was primarily a PC gamer for about 15 years with the exception of the last 2 or so. I'm now 33 for reference. 

I have always preferred the GTX x60 series for graphics cards. They're less powerful but a lot more affordable. That said, my PC is also a workstation and not strictly a gaming PC.

It's not just gaming, I use my computer for pretty much everything so this time I want something strong instead of buying something already pre-made that's obsolete the minute you leave the store, I won't go fucking crazy updating every years, I just want something that will last and need be that I can upgrade if the performances slow down. And also I like building stuff so I welcome the chalange and the knowledge I will get from this. thx for your inputs tho

So you already have a PC? Then you can save a lot of money if you only replace the parts which are too slow and reuse the rest of the components.

When I upgraded from my 2006 setup (Core2Duo E6600, DDR2 RAM, 8800 GTX), I only switched the CPU (Core2Quad 9550) and the GPU (GTX275 then GTX580) until 2013, the rest stayed the same.

In 2013 I switched the mainboard and CPU (i5 -4670k) and RAM (DDR3) and added an SSD, last year I switched the GPU again (GTX 970), the rest stayed the same.

So I still use my 2006 case, power supply, DVD-ROM, HDDs (additional to the SSD), monitors, peripherals (keyboard, mouse, 360-gamepad, 3D-vision...), no need to waste money to replace these components.

it's a mini case, I'll put it in the familly room. But I have already an other monitor, I might use the dvd-rom but everything else is obsolete

My only advice is invest in more memory then enjoy all the mods you can in fallout 4.