Upload your own extensions to a server?
 

How would you use a uploaded extension and or compile them. When you don't have root access to the server.

You wouldn't, that would be a major security hole.

i mean, how would you upload a custom extension to the server and use it? Or you just can't?

You have to edit the php.ini file. Although you can try dl().

If it needs to be compiled and you don't have the necessary access, then your hosting provider might compile it for you. If the extension is a popular one (from PECL perhaps) then chances are there is a version available pre-compiled that you can just throw into the extensions folder (its location depends on the setting in your php.ini), enable it (again in php.ini) and restart the web server to load it in. You're probably out of luck if it's your own extension and your host won't give you shell access (note: you don't necessarily need root access).

Your use of the word "custom" in this instance seems to be confusing matters. Custom as in home-brewed, or custom as in not-installed-yet?

yah PECL extensions :)...