Where can I download free Architecture Software?

Sketchup

• There is a Free version which is really excellent.  You should start there: http://www.sketchup.com/download/
• Eventually you may need to upgrade to Pro, but you should be able to get by with the free one while you're learning.  Also, the pro version gives you 8 hours of working time before you have to pay for it.

Autodesk Products (AutoCAD, Revit, 3ds Max Design):

• Pick any Autodesk software and you can download a 30 day trial: http://usa.autodesk.com/products/free-product-trials
• If you are a student or instructor you can get a 14 month free trial of all Autodesk software here:  http://students.autodesk.com/
• If you're ready to buy, you can buy the software online, and I'd recommend buying one of the suites if you need more than one Autodesk tool:  https://www.autodesk.com/products

Adobe Products (Photoshop, Illustrator & InDesign):

• This also has a free 30 day trial: http://www.adobe.com/cfusion/tdrc/index.cfm?product=photoshop&loc=en_us
• All of the Adobe Tools are now offered on a subscription plan, which makes it much much cheaper than before.  If you are a student or instructor you can get all of them for as little as $30 a month, otherwise its $50/month: http://www.adobe.com/products/creativecloud/buying-guide-education-discount.html

Rhino 5

• This has a 25 save trial that you can download and install here: http://www.rhino3d.com/download
• When its time to purchase you can buy the full version which is $995 for a commercial license and $195 for an educational license: http://www.rhino3d.com/sales/north-america/United_States

Grasshopper

• This is a free plugin to Rhino that you can download here:  http://www.grasshopper3d.com/page/download-1
• Make sure you download the one that matches up with the version of Rhino you're using 4 or 5.