For once I've got a building that turned out sort of all right, so that's exciting, and I'm looking for some feedback on it. As an intro, I built a lounge on a 20x30 lot (it uses up all but a few squares of lot space) and tried to incorporate a sort of industrial/natural theme. So there's a lot of concrete and metal as well as wood and plant life, plus a few water features. There is a raised bar and a sunken dance floor, and as a whole it's quite open and spacey (if it is just a large box). It uses only base game and Late Night objects, so I had to stretch a bit for decor. I'm thinking fusion lounge fits it the best, so that's what I'm going with.

Now, onto my thoughts. Click through for the album. Some pictures are a little older, so current images will be noted.

• Floor and wall style. I've never been good at picking out walls and floors. There's brick on the main floor, metal on the bar floor, fancy stone in the bathroom, and cobblestone on the dance floor. Walls are pretty much just brick and concrete with metal-framed wood for columns. It just seems so...plain, I guess.
• The exterior. Yeah, it's a box. A big concrete and brick box. The one side with the large windows seems fine, but I don't know what to do with the rest. I added some windows behind the bar, but I don't think it looks quite right. Should I try breaking it up with a better texture or more/different windows? Besides those two walls, the rest are totally blank.
• The theme as a whole. I think it works in a weird way, but I wanted other opinions on it. The decor is limited and a little random, so I'm worried it doesn't look good. There's also the blank area around the bar. I thought about filling it with something like plants, but maybe that'd be too much?
• Other things. I'm adding some ductwork and I'm thinking of making a catwalk or trusses on the second floor for decoration. Is the dance area all right and is a dance floor fitting, or should I replace it with something else (like a stage)?

That's about all I've got off the top of my head. I'm new to this, so I hope I'm not shoveling too much useless info into the post. These were the specific things I'm either having trouble with or want feedback on, if anyone's willing to provide it.

I really like the interior that you've got. The only issue I really have is, as you mentioned, that the exterior is just a big box. If it were my game, I would probably go with a couple of sections of low half-gable roof instead of a flat roof to give it a touch of texture there. The front looks good. If you could lose a little space on the side, I might would pull the upper wall back a couple of tiles in order to create a balcony. Your building would still be square but then you could add some seating, lights, plants, etc to liven it up.

Good job
Now here are some suggestions:
1. You may want to consider adding one more accent colour for the exterior walls, eg a darker grey to highlight the odd-numbered windows on the plain, flat wall, so as to give it a bit more texture (considering that you are working near the lot edge, if not, I would extend one tile out for those windows to highlight the structure)

2. For the roof I would suggest adding the free, patched-in air conditioners, and using patched-in solar panel flooring on the rooftop to give it an industrial feeling with all the pipes, ducts, machines and so on, on the roof. I suppose you have LN? You can add some on the exterior walls.

3. I suppose you didn't recolour the brick wall? Go for a darker version. Same goes with the light grey wall, you may also want more grungy textures in CASt.

4. For interior, the two-stories lobby, try to do adequate lighting for both floors since TS3 doesn't support multifloor lighting at the moment.

5. If you want to go with a modern, industrial feeling, add some boxed plants (such as bamboo or some shrubs), with some pebble terrain paint underneath (plus dirt blended in) on the exterior, so as to up it into a lounge. Right now it looks like a poorly maintained lounge.

6. Awesome dance floor, I really like your idea of using fences as a overhang!

7. Since I have an OCD with CASt, to give a suggestion, I would highly recommend CASt most (if not all) of the things to go with a coherent tone (eg darker concrete walls in toilet, removing the blue accent for the flooring). You want to add in a vibe of fresher colour to accent up the areas (eg red + gret + little white + black)

8. I think the stairs down to the dance floor are a little odd. The idea of dance floor not on the same level as the main lounge area is GREAT! What I suggest is adding some plants to line around the dancing area (so that besides the stairs there should be some plants).

I think I wasn't being clear enough on my wording, dunno if you get what I mean.
Just good luck and try your best, it's a great job!

Thanks so much for the feedback! I've been working on other non-Sims related stuff lately, but I'll be getting back to it soon enough. For right now, my thoughts re: the suggestions.

The building is right up to the limit, so I'd have to drop it on a bigger lot to expand. It's probably not a bad idea, since I could do landscaping around it to tie in with the interior, bump out the windows, maybe have a outside porch seating area? But as it stands now, yeah, any space would have to be taken from the inside. I don't want to make the building itself bigger. Plants are a good idea, but they might be a little too close to the building otherwise.
I didn't CASt as much as I should have, mostly did it in the bar, mostly because I didn't know where to go with it. The bathroom floor is a bit of a glaring mistake though. I'll make sure to do that before I get new pictures, and the suggestions really help. I originally added buydebug lights on upper levels, but I thought it seemed too bright. I'll give it another shot.
I had a single, large stretch of stairs leading down to the dance floor at first but wanted to try breaking it up. I'll try changing those up a bit (and try a different style in addition to adding plants). I got the idea of using fences from thesimsupply's build videos. They sit above the floor tiles but with OMSP I was able to raise the gobo enough to hang right under it.
As for the roof, I'll definitely try those suggestions. I tried adding solar panels before and they looked a little odd, but with some angles they'll probably fit better.
I'm liking the balcony idea, though I also wonder if it'll make the inside seem less open. There's a large blank wall across from the windows (over the dance floor) that might work with it, though, unless I do the bigger lot idea and do it on the outside? I might try a few things and see what works out.

In any case, thank you again for the help! Like I said, I've been doing other things and haven't been playing Sims lately (plus my computer doesn't like it very much, so I don't run it too often anyway), but I'll likely get back to it soon and do an update post when I'm ready.