Autodesk has listed their system requirements for each of their programs and versions their website: https://knowledge.autodesk.com/support/autocad/learn-explore/caas/sfdcarticles/sfdcarticles/System-requirements-for-AutoCAD.html
They also have some recommendations listed, which I would go with. Depending on how long you are planning on using this software or planning to upgrade it will make a difference whether to buy a laptop or desktop.
The big advantage of a desktop PC is, that you can add "better" or "newer" parts as soon as the current ones don't hold up anymore. This can become a problem with a laptop, when you either choose to upgrade the software or get larger projects, as it's more complicated to add new hardware to a laptop.
The following can be found here: https://knowledge.autodesk.com/support/autocad/learn-explore/caas/sfdcarticles/sfdcarticles/System-requirements-for-AutoCAD-2016.html
System requirements for AutoCAD 2016
Operating System
Microsoft® Windows® 10 (requires AutoCAD 2016 SP1)
Microsoft Windows 8/8.1
Microsoft Windows 7
CPU Type Minimum Intel® Pentium® 4 or AMD Athlon™ 64 processor
Memory For 32-bit AutoCAD 2016:
2 GB (3 GB recommended)
For 64-bit AutoCAD 2016:
4 GB (8 GB recommended)
Display Resolution 1024x768 (1600x1050 or higher recommended) with True Color
Display Card Windows display adapter capable of 1024x768 with True Color capabilities. DirectX® 9 or DirectX 11 compliant card recommended.
Disk Space Installation 6.0 GB
Pointing Device MS-Mouse compliant device
Media (DVD) Download and installation from DVD
Browser Windows Internet Explorer® 9.0 (or later)
.NET Framework .NET Framework Version 4.5
Network Deployment via Deployment Wizard.
The license server and all workstations that will run applications dependent on network licensing must run TCP/IP protocol.
Either Microsoft® or Novell TCP/IP protocol stacks are acceptable. Primary login on workstations may be Netware or Windows.
In addition to operating systems supported for the application, the license server will run on the Windows Server® 2012, Windows Server 2012 R2, Windows Server 2008, Windows 2008 R2 Server editions.
Citrix® XenApp™ 6.5 FP1, Citrix® XenDesktop™ 5.6.