Personally I've always preferred wooden enclosures with front access for bearded dragons. I know the all glass tanks with a top screen are popular in the US but I think they have far more disadvantages to them than the wooden ones do. The wooden / front access enclosures are far superior for maintaining stable temperatures and they allow your dragon to feel a lot more secure as three sides of the vivarium are enclosed. One of the most common forms of stress in dragons is being able to see all around which can make them feel less secure and can increase the likelyhood of glass surfing.
In terms of ventilation you want to have vents towards the top of the vivarium (on the rear wall) at both ends to promote a good circulation of air via convection and at least one vent towards the bottom of the vivarium too. You can place the bottom vent centrally if you like. Make sure these vents have insect proof covers and are fitted securely because you don't want either your dragon or its insect prey from getting out. The good thing about this set up is if ever you suffer from high humidity problems then fans can be fixed at the back of these vents to push in air at the cold end and extract it at the warm end. These fans would need to be affixed to a suitable hygrometer though.
If you want a top fitted basking light then its easy enough to cut a circular piece out of the ceiling and then cover it with mesh. A dome fitted bulb can then be affixed above the hole. I would recommend you fit your UVB tube internally inside the viv (preferably central on the ceiling) with a good quality reflector and then arrange your decor to achieve basking spots at the correct height for the tube. (You can never be 100% certain how much light is being filtered out from a UVB placed on top of mesh without a good quality solar meter)
Personally I would get proper glass for doors, which should be cheap enough from a local glass supplier because not only do they insulate better than plexiglass they are going to be a lot more scratch resistant and look better long term.