我去了泰国。

我去了泰国。我看到了很多非常好漂亮的建筑物。可是我不能看不到了象。我很悲哀。真可惜。

Nice job! Just a few notes:

1. We usually don't use 好 to describe buildings. You can use something like 漂亮 or 壮观 instead. 

2. 我很悲哀 literally means "I am sad", but the "sad" means you're <em>grieving</em>. I would simply say something like "What a shame", which is 真可惜 in Chinese. 

Hope this helps, Musha! 

我去了泰国。

我去了泰国。我看到了非常多的漂亮的建筑物。可是我没能看到大象，我很伤心。

我去了泰国。

我去了泰国。我看到了很多非常好的建筑物。可是我没能看到大象。我很难过。

我去了泰国。

我去了泰国。那里有很多非常漂亮的建筑物。但是我没有看见大象。我很悲哀！

我去了泰国。

我去了泰国。有我多非常好看的建筑物。可是我沒有不能看了到大象。我很/失望/可惜悲哀。

建筑物 can also mean construction materials!  I assume in English, you are trying to say interesting buildings.  In Chinese, you need to be more specific in order to write better.  Given the context, I assume you saw the palaces and temples.  You can say,

有非常华丽的宮殿和殿堂

佛堂 would be better since the temples are Buddhists.  In Japan you have the differentiation between宫 and 寺.

失望 = 失望した

可惜 = 残念ながら