For the first century of its construction - from 1882 to the 1980s - it was financed only with donations, which resulted in a rather glacial pace of progress. Then in the 1980s they decided to count the entry fees paid by tourists as "donations", and considering the enormous popularity of Barcelona in the past decades as a tourist destination, the pace accelerated accordingly. But still it's not comparable to some skyscraper that's built by some company that has all the money it needs to do so from the start.

There was a picture in our newspaper of what's there already and what still needs to be added. Basically, the ship is largely finished now, and so are a number of towers (there'll be fourteen towers in total, one each for Christ, Mary and the twelve Apostles), but all of the main towers, including the enormous Christ tower in the middle, have yet to be built, as do the frontal façade and some smaller things.

The article also mentioned that the cathedral of Cologne in Germany took, iirc, 632 years to be fully finished, so this isn't even remotely near a record.