I didn't express that very well; using the infinitive form of the verbs didn't help. What I ought to have said was that I think maybe it can be expressed as

"Я заканчиваю работу.." - "I am finishing work"
"Я заканчиваю работать.." - "I am finishing working" (maybe finishing working on/as something)
"Я закончу работу.." - "I will finish work"
"Я закончу работать.." - "I will finish working"

My point was that "работу" is the noun 'work' in English, and "работать" after another verb would be "working"; which would (I think) count as a verbal noun in English.

"Я буду заканчивать" - "I will be finishing" -yes, I think this correct, it's certainly good English.

"Я заканчиваю" - "I am finishing/I will finish" (present/future via "сейчас", "завтра" or context) - This is interesting; could one say "Я заканчиваю работать/работу завтра" to mean "I will finish working/work tomorrow"?
From what I have learned so far, I would want to say "Я буду заканчивать работать/работу завтра", or "Я закончу работать/работу завтра".