ROOFTOP TENT BUYERS GUIDE

Canvas vs. Polyester

First off when looking at Roof Top Tents the materials are what makes the difference. The less expensive tents are lighter weight and use a nylon material. Where the more expesve tents use a polycotton canvas. 
Polyester is a popular choice, because it is cheap, and it performs well in various weather conditions. Polyester is the most common fabric used in tents. Although it is not waterproof (unless coated), it doesn’t change shape when wet (unlike nylon) and does not perform too bad in sunlight.
Poly-cotton is a blend of cotton and polyester. While keeping all the good qualities of cotton, it has some of the benefits of polyester tents. The main fabric is cotton, with polyester in the weaves, so it inherited some of the mildew-resistance, it is stronger and less likely to rip than pure cotton. Poly-cotton can be left uncoated but usually there is a coating applied to repel water. Its durability, breathability and weather resistance make it great for family camping tents, swags and roof top tents.
GSM (grams per square meter), refers to the weight in grams of one square meter of raw woven canvas or polycotton canvas. (Also still measured in ounces per square yard as well.) A higher gsm means a higher fabric weight and thickness. Most tents range from around 280gsm to 380gsm with more modern polycotton canvas closer to the lower end.  

Soft Shell Rooftop Tents

Soft Shell Rooftop tents are the most popular of all the roof tents. The reasons are price and size. 
Size:
Soft Shell tents will fit any vehicle roof or truck bed  based width of tent. 
Soft Shell tents come in sizes of 49" to 94" The size is width (front to back of vehicle) of the tent. The tent folds out and doubles the width. Most tents are between 48"-50" folded so unfolded you will be  (tent size) by 100". 
Look at the size comparison for perspective of size.
49" is a Standard Bed (1) person
55" is a Full Bed (1-2) people
62" is a Queen Bed (2-4) people
72" is a King Bed (4-5) people
87"-94" is a Giant Bed (5-8) people. 
The people count depends on the size of the person but most have at least half as children. 
Price:
Soft Shell tents are priced between $1000 on the low end and $3000 on high end. This is relative lower than the hard shell tents and accommodates more people. 
Soft Shell Tents use a PVC transport cover that either zip or straps over the folded tent. This can add a few minutes to your close up time but is fairly easy and takes minimal effort. The transport covers last up to 5 years if left on you vehicle full time and cost under $150 to replace.  

Clam Shell Rooftop Tents

Clam Shell Rooftop tents generally open on the front end of the tent similar to a clam. The exception is the iKamper Skycamp and the FSR Odyssey which open on the side of tent.
The shell of these tents are made of fiberglass, aluminum and ABS plastic. The hard shell gives greater areo-dynamics and more protection. 
Size:
Calm Shell tents have vehicle fitment restrictions. All are 80+" long (with exception of iKamper mini 48" wide). If installing on truck bed need cab height bed rack.
Most of these tents are 48" to 50" wide and 85" or so long and accommodate 1 to 2 people. The iKamper Skycamp 3.0 opens like a clam to the passenger side and folds out like a soft shell tent and is king bed size. 
Price:
Calm Shell tents are priced between $3500-4500.

Hard Shell Rooftop Tents

Hard Shell Roof Top Tents have the same encasement (Aluminum, Fiberglass or ABS plastic) as the clam shell but they pop straight up. The advantage to this is equal headspace and 360 degree views.
Size: 
Calm Shell tents have vehicle fitment restrictions. All are 80+" long. If installing on truck bed need cab height bed rack.
All Hard Shell tents are between 48"-55" wide and 85'"long with accommodations for 1 to 2 people. 
Price:
Hard Shell tents are between $3500-$5500.

Rooftop Tents