There are many different types of tents available today, and not just different sizes, different strengths, different shapes, and different levels of water resistance. You need to identify your exact requirements before choosing a tent, otherwise, you could end up with a tent that does not meet your needs, or too expensive for what you will use it for.
Well, then you will probably need to look at getting something with a really strong pole, such as aluminum, fiberglass pole is not standard. You can also purchase good quality army tents online for camping, hunting, or as temporary shelters.
Waterproof tents lose their quality over time and will need to be re-proofed. Thus, the higher the number, the longer it will last before needing reproofing, and the better it will be when it is re-proofed.
Most of the serious tent double-skinned these days. The idea is that if the water will pass through the outer layer, it will run down the inside of the outer layer without reaching the inner layer, thus keeping you dry. If water gets into a single skin tent, water will run into the main compartment and you will get wet.
A single-skinned tent is fine to use a minimum though, where it will remain waterproof. They are ideal for a festival where you just wish to use it once before it will actually destroy anyway. If you are going to keep the tent in your car when traveling around, heavy tent largely unimportant.