-ㄹ 거예요 and 려고 하다 are similar but there is a difference with the meaning. -ㄹ 거예요, you know is the form used for future tense, simple as that. But 려고 하다, may have the inclination that it will be done in the future, has an intention behind it. You can think of it as "planning to..." Ex: 다음 주에 손목시계를 살 거예요. ( I will buy a watch next week.) 다음 주에 손목시계를 사려고 해요. (I am planning to buy a watch next week) The first one implies that you will buy a watch next week, that you are set to buy one. But the second sentence implies that you may or may not buy a watch next week, but it is in your plans that you will. I hope you get the point. ^^

I'd say ㄹ 거예요 has the nuance of "I'm going to (do something)", and (으)려고 하다 has the nuance of "I intend on/plan to (do something)".

I welcome these kinds of questions. It show itself how different Korean and English are and how hard each foreigner acquire it. :) For natives, two of them are almost same. Like "Will and be going to " but I think that will and be going to has slight difference and it's used in some different way. By thinking this way its a same process in ~ 할거에요 and ~하려고 하다

there is a slightly different usage associated with -려- that you should be aware of. certain things that are on the brink of happening (becoming imminent) would fit the bill of using 려. example... you are sniffing and feeling tired, and you feel you are on way to have a full-blown cold. In situation like this. 려 can be used.