You can assemble a 1911 if you have moderate skills.
Your FIRST move is to buy a copy of Jerry Kuhnhausen book "The Colt .45 Automatic: A Shop Manual, Volume One".
http://www.brownells.com/.aspx/pid=13805/ttver=2/Product/JERRY_KUHNHAUSEN_THE_COLT__45_AUTOMATIC
Your second move is to get a copy of Brownell's catalog. They sell everything you'll need.
Advice: For your first build assemble a working 1911 without any custom features.
Figuring everything out is made much harder when you're also trying to alter things to include custom features.
Match parts and custom feature parts almost always require significant fitting.
Build a working gun first, then add the custom items later, or build a second gun with all the custom stuff.
For the first build, stick with name brand, quality parts from Brownell's.
Cheap kit parts, gun show, and Shotgun News parts are all cheap castings.
They're all out of spec in some areas, and trying to figure out why something isn't fitting or working correctly is only made all the harder when the parts are substandard.
When the parts are out of spec, the mis-fit tends to "stack" and get worse as parts of the assembly are added. This can make it extremely difficult to figure out what's wrong.
Name brand parts are in spec and will usually require minimal fitting.
Once you've built a properly working 1911 and know how the gun works, then you can branch out to custom items and fitted Match type parts.