@simvasion There are a couple things going on here. First, the issue with being unable to spray graffiti (but not paint a mural) on an indoor mural is a separate issue from interior snow and clearly a bug (or, more likely, careless coding). You can put a mural in a basement that is completely under your building and if there is snow outside you cannot paint graffiti because "There is snow covering the mural!".
Second, many of the EA buildings in the game are not properly winterized. Not just snow on the floor, but sims are cold even with a thermostat in the building. This affects both community and residential lots. Many of the buildings are not built correctly; for example, rooms as defined by the game include both interior and exterior spaces, making it impossible to add ceilings. These buildings can require a lot of rebuilding to winterize. Also, some buildings with "correct" rooms lack ceilings over some rooms, so you need to check for that. The EA builders also seem to like to add a lot of invisible fences to roof areas which also make it difficult or impossible to add ceilings. Some of this is due to the lack of a proper flat roof option (how hard could that be??), but in many cases they serve no discernible purpose and can be deleted. Note that roofs over rooms without ceilings may or may not seal out the cold (depends on the building).
The two buildings mentioned in this thread are both problematic. The gallery in particular needs a lot of work to close in the interior spaces. I ended up rebuilding some walls and putting a glass roof overs the multi-story sections. There is one residential lot I was never able to get right and ended up cheating the iceproof perk for all the residents so that they didn't need to move out. Of course, all the buildings that have open roofs (like the gym and lounge in Uptown) need to be reconfigured to have roofs. The least EA could have done is post winterized versions of their own buildings in the Gallery for download, although I sometimes wonder whether the folks who do the building even know how to fix their own buildings—so many of the buildings that come with the game and DLC are so incompetently designed and built.
There are a lot of issues about the way that weather was not incorporated into the rest of the game very well: Rain at the festivals, invitations to the ruins or the bluffs during blizzards, etc. More careless coding (or lack of interest).
