There are two things related to the original question that are in order to be addressed. First, the idea of 'average Soviet citizen' is a pretty vague term, given rather substantial disparity of standards of living between various social groups in the USSR. Rural population, especially people in kolhozes (collective farms) lived in pretty simple conditions while urban dwellers, although largely also far from being well-to-do had it better with steady access to most common amenities. It should also be noted that the living conditions differed strongly also in cities - common people, such as rank-and-file workers usually lived in 'communal flats', usually re-purposed townhouse flats with each of the rooms being occupied by a separate family sharing the kitchen and bathroom. This was at least partially due to large influx of people to cities during the NEP and industrialization under Stalin and after 1945 also due to shortages of living space resulting from wartime destruction. This changed in Khrushchev's era thanks of statewide construction programs, although even then majority of urbanites still lived in relatively small apartments in the tenement blocks sometimes using a dacha (summer house) on the outskirts of town. But there were people who lived in much better conditions - high-ranking party officials, renowned scientists, various specialists or award-winning artists quite often were being given a flat, house or summer house as a reward ('given' being a somewhat misleading term, as the buldings were state property and beneficiaries could only live there and prior to 1948 Soviet citizens were not even allowed to legally own real estate). This means that a famous or well-connected person in USSR could have enjoyed much better life standard than the common folk, at least in Stalin's era.

Since 1941 Stalin held positions of the General Secretary of the CPSU and Chairman of the Council of Ministers of the USSR, meaning that he was the equivalent to both Prime Minister de facto President, so factual dictatorial power aside, we can say that he was the highest official and single most important person in the USSR. The fact that he could count on the better conditions that most of his countrymen would go without saying, but given the sheer amount of power he wielded, official or otherwise, Stalin wasn't that much interested in luxuries. Technically, he could have demanded anything and his demands would have most likely be met immediately, but besides several luxury houses, Stalin seemed to be not to concerned with material benefits that came with his political power.

When working in the Kremlin, Stalin lived in a small apartment specially made to suit his needs. It was few small rooms, separated from the rest of the building with heavy doors and several military checkpoints. Being very suspicious (some historians even suggest borderline paranoia), Stalin usually tried to reduce contacts with other people, especially those he didn't know very well and considered personal safety a paramount thing. Similar self-contained apartments were also located in his Kuntsevo residence. According to contemporary accounts, despite living in luxury, Stalin was known (by those who knew him so close) for general disregard for comfort, staying for long hours in his office and sleeping on a couches, despite having many bedrooms to use.

On the other hand, he liked to eat and drink well and enjoyed long parties with his colleagues and selected guests. According to some accounts he sometimes partook in hunting with other Party officials. Stalin was also very fond of southern USSR (especially his native Georgia) and usually resided there for 3-4 months a year save for the period 1937-1944, when he resided solely in Moscow. To enjoy the trips mentioned above, Stalin, he had several houses that were effectively quite opulent residences, especially his main house in Kuntsevo (now part of Moscow) he ordered to be designed and built in 1926 (this was also a place of his death). This was not only Stalin's primary residence but also and unofficial centre of power, parallel to Kremlin, as the leader of the USSR conducted a lot of meetings with other high-ranking Party officials and other politicians there. This residence, was maybe not overly grandiose and decorative, but modern and functional, sporting various luxurious facilities (movie screening room, swimming pool, state-of-the-art music equipment etc.) and run by staff, usually hand-picked by Stalin himself. Apart from mansion in Kuntsevo, Stalin also used (he technically didn't own any of these real estate) several other houses close to Moscow (in Lianozowo, now part of the city proper), Crimea (Yusupov's Palace in Khoreiz) and Georgian SSR (in Gagra, Bagripsh, Akhali Atoni and on the shore of Ritsa Lake). These houses, although smaller than Stalin's house in Kuntsevo were still mansions of considerable size (especially Khoreiz palace and villa in Gagra), tastefully furnished and usually surrounded by large parks or gardens.

So, to sum it up, Stalin enjoyed vastly better standard of living than an average Soviet citizen or even many of high-ranking Party officials, although this stemmed from his actual political power and bureaucratic model of the state rather than hoarding private wealth.