The roll out awning is usually mounted from the pop-top section of the roof of the caravan.  This means you would have to unclip the catches that secure the roof to the body and release the rollout awing prior to raising the roof.  Once inside, you would lift the roof and secure the brackets that hold it up.  Most pop-tops also have gas struts that assist in this process.

Advantages –

• It is reported that, as the van would have a lower profile, it has less wind resistance but some tests have revealed there is little difference overall.
• Good ventilation.
• They can be lighter to tow depending on how the van is accessorized.
• Low centre of gravity which should assist stability on the road.
• Due to its lower profile, it may fit more readily into a garage or carport.

Disadvantages –

• Can take longer to set up.
• If stopping for a rest and a ‘cuppa’ it is more likely you will have to stoop down whilst inside or go to the trouble to raise the pop-top’s roof.
• The door height is lower and you may need to watch you don’t knock your head.
• There will be no overhead cupboards but rather a row of cupboards that would be lower and these are likely to be smaller.
• If there is a shower facility inside then the top section of it will most likely be vinyl and this may be more difficult to keep clean.
• If you want to have solar panels on the roof there may be a weight limit or you may have to have stronger gas struts.
• The air conditioner is likely to be a ‘split system’ as it is not common for it to be mounted on the roof due to its weight. 

Caravan Types (General)
Different types of caravans. Pop Tops, Full Height, Off road, Cross Country. Which one is right for you? Advantages and Disadvantages

Full Height Caravans
These vans have solid sides and roof. What are some of the advantages of a full height caravan over a pop-top caravan.

Cross Country Caravans/ All Terrain Vehicles (ATV)
Off-Road and ATV Caravans are designed to withstand travel on corrugated roads as well as for self sufficiency when it comes to water and power.

Also see:

Best Tow Vehicle
Different Types of Caravans
Hitches, Anti-Sway Bars & Chains
Fifth Wheelers
Caravan Reversing