Portal/1.03

Daemon
The Portal is the Daemons' main research building, offering a broad range of differing skills, including a seriously important one - Binding. The skills researched from the Portal all have large affects on the Daemon race and the building is also required for the production of Succubi, which all makes the Portal very important and thus should be of high priority to build. Although, if your opponent lacks the Banish spell (which is quite likely) then you could build the Gallows ahead of the Portal for those very useful income skills. The improved income would also help out with the expenses of the researches found at the Portal.

The Portal also offers a large +4 points to your army limit that could help support the usually large Daemon units, but, despite being about average in size, it's terrible shape makes them undesirable to build - leaving many pockets of wasted space and potentially trapping your builders after completion when built too close to another object. Further more, going through tier 3 and 4, the Daemons can build Lightning Spires which, when upgraded, offer +3 army limit points as well as acting as a powerful secondary defensive structure. This pretty much means the Portal shouldn't be used to increase your army limit.