Roosevelt approved of every proposal Stalin made.
A broad outline of the behavior and proposals of Roosevelt, Churchill, and Stalin at Tehran can be found in the diplomatic papers published in 1961 by the State Department, in a volume entitled Foreign Relations of the United States: Diplomatic Papers: The Conferences at Cairo and Tehran 1943.
As to specific agreements on the postwar division and occupation of Germany, the Tehran papers reveal only that the European Advisory Commission would work out the details.
We know that Roosevelt and his military advisers in November, 1943, agreed that America should take and occupy Berlin. Yet, 17 months later, we did just the opposite.
In the closing days of World War II, the American Ninth Army was rolling toward Berlin, meeting little resistance, slowed down only by German civilians clogging the highways, fleeing from the Russians. German soundtrucks were circulating in the Berlin area, counseling stray troops to stop resistance and surrender to the Americans. Some twenty or thirty miles east of Berlin, the German nation had concentrated its dying strength and was fighting savagely against the Russians.
Our Ninth Army could have been in Berlin within a few hours, probably without shedding another drop of blood; but General Eisenhower suddenly halted our Army. He kept it sitting idly outside Berlin for days, while the Russians slugged their way in, killing, raping, ravaging. We gave the Russians control of the eastern portion of Berlin–and of all the territory surrounding the city.
To the south, General Patton's forces were plowing into Czechoslovakia. When Patton was thirty miles from Prague, the capital, General Eisenhower ordered him to stop–ordered him not to accept surrender of German soldiers, but to hold them at bay until the Russians could move up and accept surrender. As soon as the Russians were thus established as the conquerors of Czechoslovakia, Eisenhower ordered Patton to evacuate.
Units of Czechoslovakian patriots had been fighting with Western armies since 1943. We had promised them that they could participate in the liberation of their own homeland; but we did not let them move into Czechoslovakia until after the Russians had taken over.
Czechoslovakian and American troops had to ask the Soviets for permission to come into Prague for a victory celebration–after the Russians had been permitted to conquer the country.