A three season tent will do just fine, unless you plan on camping on some exposed mountainous peaks.
You'd want at least a 2 man(barely adequate for 1 person), preferably a 3 man(little more 'elbow' space and height but bulkier), or if you are hauling a trailer,(or going solo and don't mind packing it on the passenger seat ortour box rack)a four man or larger for the ultimate in space/height.
Something with a fuller coverage rain flysheet will protect you more than one with a small 'umbrella' type of rainfly sheet.
To make it truly water repellent, expect to spend some time sealing the stitching on the fly sheet(unless taped) and the floor seams. I highly recommend using McNett Seam Grip to seal the seams. http://www.rei.com/product/603034
After applying, let dry for at least 5-8 hours and then 'dust' the seams with a light
dusting of Talc/baby powder to prevent it from sticking to itself, or other parts of the tent.
Make sure it has some sort of ventilation, such as windows/doors with mesh. 2 doors are better than one, especially for 'cross ventilation'
As to where/what brand to buy, it depends on how much camping you plan on doing. Wally World would probably do fine for a couple weekends a year, or if you plan for lots of camping, in some serious conditions for a few years, look for a more reputable outdoors retailer, such as REI, EMS or if you have a local outdoor shop in your town, ask them for their thoughts/advice.
Most importantly, if you are 6' or taller, make sure you fit inthe tent when you are laying down in, without your feet/head touching any of the wall ends.