First of all, "I am sleeping" is "Я сплю". "Спаю" is incorrect.
You should say "Я скоро буду спать". "Буду" is something like "will". "I will do something" is equal to "Я буду делать что-то".
You should capitalize "я" only if it is placed at the beginning of the sentence. Names are always capitalized.

Correct my mistakes please.