This whole issue of increasing the maximum file size of a PHP upload is probably one of the most frequently asked, and answered, questions in these forums. You will find many threads dealing with this - just use the search feature of the forum.
A complete custom php install is a bit of an overkill for simply adjusting your max_upload_file_size, and is much more complicated than what you need to do to achieve that goal.
I suggest just using the default DH install of php with your own custom php.ini file to change the size of files you can upload with PHP.
It is a much simpler process to complete, though you will need shell access and a basic understanding of what is going on in the nix shell.
Frankly, I fail to understand why so many inexperienced users seem to think this is necessary or desirable - there are loads of free perl scripts out there that are easy to install that do not limit the size of a file upload and you always have ftp available for uploading. At any rate - the above paragraph points you to the easiest way to do what you want. Good Luck!