Building a custom computer

Perhaps if you list the needs we could help. Lenovo customizes my computers very nicely, so that is one source.

CPU i7 NOT xeon.
32 GB memory
1080 Ti 11g graphic card.
x1 ssd 500gb x1 tb sata

Preferably small form case but also tower is ok.
Has to be WHITE case.

Thank you for updating. I will watch for such as supplier. "Has to be WHITE case"  Lenovo are Black.

While we wait for other answers, here is a list of the top five builders. The last one appeared to have white cases.

https://lifehacker.com/five-best-custom-pc-builders-1664766332

Just FYI, the 5th company there

Origin PC... I heard some negative reviews on them.

Yes. From a business perspective, the builder needs to have enough business to be profitable and that can be hard.

For example (and just discussion) this Lenovo P900
http://www3.lenovo.com/gb/en/workstations/p-series/ThinkStation-P900/p/33TS3TPP900
has Xeon CPU, 16 DIMM slots (so more memory than you specify, Graphics are a selection of Nvidia, you can easily get 1 TB sata hard drives (my own M73 has two of these) and new machines all take SSD.

So it actually gets close but of course, not exact.

it's for a proprietary software, so it's has to be kind of exact.

You will probably have to locate a small, local "white box" assembler in your area. I use PLE, I was able to easily configure a machine matching your specs exactly. Might be tricky if you live outside of Western Australia. The most difficult bit might be  the white, small form factor case. Not a technical thing, more a fashion problem. I have not seen a plain, small form factor white case for ages. Some flashy cases aimed at kids to play games on are white, but generally have other garbage like flashing LEDs and glass panels.

I would be VERY surprised if the supplier of your software does not support a machine with black paint.

https://www.ple.com.au/Custom-Built-PC/627428/PLE-Home-Basic-Custom-PC-System

i would build it for you - but as said  - the white box can be difficult to find
but you'll have to be around Belgium then

another option can be : let them build the black box - and change it into a white one yourself?

Are there some small local PC shops? Here we have some they built according to your needs.

"let them build the black box - and change it into a white one yourself"

LOL, reminds me of a site years ago, where we had to provide red machines. (it was a nightclub). Took a while and lots of spray paint, but I managed. The old CRT monitors were trickiest, everything had to come apart.

Nothing really unusual about this, other than a small white case.  If you could find the case, it would be easy enough to build yourself.   If you have a microcenter nearby drop in they will give you a hand and they have quality mobos,  power supplys, and most other components.  

Also visit Newegg.com for components and a wide selection of cases.  
see:  https://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007583&IsNodeId=1&bop=And&ActiveSearchResult=True&SrchInDesc=white&Page=1&PageSize=36&order=BESTMATCH

The real trick, even though you can get a mini ATX mobo  (they are available with PCie 3 slots you need for the video card) is not many Mini ATX cases will be long enough to fit that card -- it looks like even some mid towers could have an issues with it.  

See: https://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH&Description=1080+Ti+11g+graphic+card&N=-1&isNodeId=1

i found white cases on amazon :
 https://www.amazon.com/Computer-Cases-White-Components/s?ie=UTF8&page=1&rh=n%3A572238%2Cp_n_feature_keywords_two_browse-bin%3A5995625011https://www.amazon.com/Computer-Cases-White-Components/s?ie=UTF8&page=1&rh=n%3A572238%2Cp_n_feature_keywords_two_browse-bin%3A5995625011

others here :  http://www.overclock.net/t/1347827/best-white-case

so it seems to be not such a big problem