They aren't fabrications.

The Soviet Famine of 32-33 (what you refer to as the Ukrainian Genocide) was an actual famine caused by a massive drought throughout the major wheat production centers in the Ukraine and North Caucuses. The debate lies in whether or not the drought was deliberate or not and the extent to which the Soviet government knew about it/was slow to react. More modern evidence points to poor relations between the Party and the peasants, and a total hatch job by Soviet scientists on actually studying the soil conditions, as central to understanding why the drought occured. Calling it solely a Ukrainian genocide would mean ignoring the affected regions of the North Caucuses, and the general impact on the country as a whole as a result of having much less wheat output.

I know there is a book that some like to cite which claims the famine was made up by Nazi's and Harvard as anti-soviet propaganda, but that argument hold little to no water. As an aside, especially with soviet history, stay far away from one Grover Furr. He isn't an historian, he's a nut who cares more about trying to protect the image of Stalin than actual research.

Further reading: jstor link to paper on party-peasant relations

paper on soil conditions and harvest statistics during the famine years

The Chinese Famine that resulted from Mao's Great Leap Forward had similar issues. Local party members lied about how much grain the villages could produce and vastly over estimated the yields. This lead to grain requisition quotas that had devastating effects, as the higher members were unaware of how little was left after taking the amount of grain that was proportional to the amount that had been reported. This was coupled by a large drought. In short, people had less food due to faulty reporting, and not enough water to grow food even to just feed themselves.

Further reading: Jstor paper on grain quotas and procurements

Stalin and the camps. I think you meant to say concentration camps, not consideration camps. I admittedly am not an authority on the GULAG system, but it has been covered here before.

The Holodomor, the term for the famine in Ukraine, is seen by many as a deliberate attempt by the Soviet regime to kill off the Ukrainians. They were quite adamant about not joining the Soviet Union, and thus it is argued that Stalin (or those close to him) ordered grain to be withheld from the peasants even when famine hit, as a means to punish the Ukrainians for their actions against the Soviet state. There is considerable evidence towards that being true, and like I noted most scholarship seems to support the view, but others do note that droughts were also a factor, and it wasn't just limited to Ukraine. But I tend to lean towards arguing that the Holodomor was, at least in part, a deliberate action (though I'm admittedly biased, as I have Ukrainian ancestry).

As for the Gulag system, Stalin didn't exactly found it, as a similar system had existed during Tsarist Russia (and Stalin himself had been exiled to Siberia on multiple occasions). Prisoners being internally exiled to Siberia, or elsewhere in the USSR, began almost as soon as the Bolsheviks took control of Russia. But Stalin definitely saw over the greatest numbers of people imprisoned in the camps, numbering in the tens of millions over his time in charge.

Mao being responsible for the Famine was somehow affirmed in the "Resolution on certain questions in the history of our party since the founding of the People’s Republic of China" adopted by the sixth plenary session of th eleventh central committee of the CCP.

"More important, it was due to the fact that Comrade Mao Zedong and many leading comrades, both at the centre and in the localities, had become smug about their successes, were impatient for quick results and overestimated the role of man’s subjective will and efforts. After the general line was formulated, the Great Leap Forward and the movement for rural people’s communes were initiated without careful investigation and study and without prior experimentation. .....It was mainly due to the errors of the Great Leap Forward and of the struggle against “Right opportunism” together with a succession of natural calamities and the perfidious scrapping of contracts by the Soviet Government that our economy encountered serious difficulties between 1959 and 1961, which caused serious losses to our country and people."

And "Likewise, responsibility for the errors committed in the work of this period rested with the same collective leadership. Although Comrade Mao Zedong must be held chiefly responsible, we cannot lay the blame for all those errors on him alone."

Source: https://www.marxists.org/subject/china/documents/cpc/history/01.htm