Future tense-when

The future tense Futurate is Prototypically=a use of the present tense, permitted in Main Clause, to indicate future time
---when--as soon as---after---
=future
eg:-
I shall be feeling really nervous (when)/(as soon as)/(after)
Or
=I feel nervous when(as soon as)/(after);
Then the predicate:-
=I end up in Rome tomorrow.
=I start visiting in Rome next week.
=I start next week in Rome.

Further eg:-
The week ends tomorrow;
Tours start next week.

Also the corresponding uses of the "preterite"
eg:-I thought that tour started next week in Rome.

2015-04-05 19:42:48 補充：
m.c.=future=present+future event=arrived+nervous=present !

What the grammar book sentence means is that
In writing a future meaning (using future tense on the main clause) with a condition (such as When, As soon as, After), the subordinate clause/sentence after the conjunction only need to use simple present tense.

The reason is because the condition for the "future event" in the sentence can only be considered "present" (not future of the future event but at the same time as the future event). So only present tense "make sense".

In answer your examples:

I will be feeling really nervous when I have got to Rome?
is Chinese thinking -
直譯是「當我已經去到羅馬的時候我便將會感覺好緊張。」
seems logicall ok in Chinese because I must have to arrived in Rome in order to foresee I will be nervous.
But in English, "have got" means you have done it = 我已經去過羅馬...而不是當我已經到達羅馬，因此英語邏輯上這句子(假設寫成這樣)是預計一樣會出現於一種經已發生了的情況中，像是時空轉移或回到過去的將來的"文學"，是不合情理的表達。雖然心理上你會對自己講「我先要到達羅馬才會有緊張的感覺，所以時間相對上"在羅馬"要先過"緊張"」，不過語文/文學表達上並不是科學，是時空感的記述，將來會發生的事的環境情況是跟那發生的事在"同時"出現的，不會有"時差"的。

You only need to remember...any condition that set up for the future tense main clause only need to be "present" with that future action, not future and not past, even though in your thoughts, the condition/situation must happen before the action.