Hi! This may be odd questions, but I’m curious and I hope you could clear them for me. Do you know when were the Water Gardens and Summerhall built? If not, can you speculate? Also, how long would it take for palaces like that to be built? Thank you :)

This one I can do. Summerhall began construction in 188 AC, and was inhabited by 209 although probably before. 

The Water Gardens began construction in 187 AC, although how long it took to be finished I’m not sure although from AFFC it seems to have taken a few years but not much longer.

In terms of general construction times, several years to several decades, depending on the complexity of construction. In these cases, Summerhall is a small and not particularly well-fortified castle, which cuts down on time, and the Water Gardens are a pleasure palace, so again you don’t need to build defenses.