A bit late, but including a SSD into your laptop is almost a must for CAD. When you are involved with large drawings that may include 100's or even 1000's of blocks/models/etc... your load up times for drawings may be in the area of 5mins and as well for your save times. If you are anything like me, you are going to be saving often. Having all of your working CAD files on a SSD can dramatically increase your performance and change that 5 mins down to 10-15seconds.
I'll agree with most of the posts also with the idea that you want a computer with maybe 8GB of ram (4gb x 2) and a good video card. Now that difference in selection for graphics cards depends on whether you will be doing a lot of rendering or not. The big difference between workstation graphics cards, and the typical gaming video cards is mostly due to rendering. Workstation cards perform significantly better when it comes to rendering. However, since you are not using Maya or programs such as that, I would suggest a gaming video card will be fine for you.
I would tend to stay away from a mac just for compatibility reasons.