Well, I hope they're not going into a genuinely random building. Just barging into somebody's house isn't likely to get much in the way of a friendly reaction, but if the PCs say "oh, I want to walk down this street" or "oh, that sounds like an interesting shop" or are otherwise pointing themselves in a sensible direction, and you haven't completely planned what's there? Sure, why not be random?
0) Random For What
But first you should have some idea what you want out of it. Everything you do should reflect off of some goal that either you or the PCs have.
Not just entering some random building for the sake of it, but, you know, looking for something particular to buy, fishing for useful rumors, that kind of thing.
And make sure this isn't something that would be covered just by, say, rolling Discern Realities and asking. Just finding a solid weapon store in an unfamiliar town would certainly be useful or valuable to you, but there's still the question of how the blacksmith is going to feel about you when you get there.
1) Random For How
So, yes, as the GM you never roll dice to make moves. Your antagonists will never be able to roll dice, consult the rules, and just make things happen without the PCs say-so. You can't roll for outcome.
Nobody ever said anything about rolling for intent, though.
That's the purpose of things like the Fourth Page Tables, so named because the stripped-down World of Dungeons version of Dungeon World only had three pages of rules. Need a prompt to keep going? Pick up the City page, roll on Population or Society, and work that idea into the situation that's already established. Or, you know, when you're looking over the list or looking up the die roll, if you see something that speaks to you, you can just use that instead. The purpose of the thing is just to give you ideas, not present some random and absolute balance.
2) Random For Why
But always keep in mind, whatever random prompting method you're using? The players were looking at you to find out what happens. So once you've got your prompt, use that prompt to feed into the GM move you lob back to them.
Let's take the simplest prompt mechanism, the one I'm absolutely sure you will have at your table: The Die Of Fate. Disguised as a humble d6, when you find yourself in need of a prompt, consider a question and roll the Die of Fate for an answer.
So, Die of Fate, is this armorsmith going to be favorably-disposed enough to the PCs to work on their armor?
6: Yes, and. Oh, there's something more? Hmm. Let me offer an opportunity that fits a class's abilities.
Clericsdottir, you mentioned your helmet was a particular make specific to the God of Craft? The smith recognizes it and her eyes light up. She makes the sign of the Turning Gears out of respect. She says it's been so long since one of the Faith has visited. ...that's kind of odd for a town this size, but you can worry about that later. You must have a lot going on, but please, sister, can you bless her tools?
Now, that's usually a pretty simple ceremony, but then people usually only have a small number of tools. Big shop like this, it'd tie you up for a whole day to do it proper, but if it's really been that long since she's had a blessing, you could also get quite a few favors out of her in return. Or you could sprinkle a little blessed water and make the sign of the Just Working in the appropriate places. That'd be the least expected of you.
5: Yes. Easy enough. Tell them the requirements or consequences and then ask.
Fletcher, you like going in first, right? Well, the smith sizes you and Rockjaw up and the people following you and grins. You're the sort of people who need the serious work done, he says, which is excellent, as he's the sort of person who likes to make serious coin for serious work.
Custom work on armor takes at least 50 coin and some time without the armor to finish the work. We can talk about the sorts of modifications you'd like once you all work out how much you're willing to spend.
4. Yes, but. Oh, so there's something in the way? Hmm. I think I'll show signs of an approaching threat.
The smith looks kind of hopeful as you look over the stuff on offer, Sir Justice, but when you ask about getting some sealants for your armor to protect against noxious vapors, her face falls. She's sorry, she says, but she can't do that. She glances significantly at the wooden icon hanging by her doorway -
looks like a long shield with crossed spears behind it. Not now, she says.
Huh. Come to think of it, you did see that sign hanging in quite a few of the market stalls on the way here. And on the armor of a few of the bravos strutting around like they owned the place. What are you doing?
3. No, but. But they could? What would make them? ...hmm, I think in this case I'll use up their resources.
When you ask after a hidden compartment in the armor for your poisons-I-mean-medicines, Shanksworth, the smith looks at you and flashes a quick and furtive sign. You get the gist of what's going on here but the countersign doesn't come to mind, sorry.
No can do, he says. He's got other priority projects right now. He thinks for a moment. Of course, if you were willing to pay an expedited processing fee, that might change.... This is going to be a significant bribe, let's call it 65 coin on top of the 50 for the custom work.
2. No. Alright. But I don't want to just stonewall them, as much as provide a path forward... ah. I'll reveal an unwelcome truth.
You put on your best smile, Stringfellow, but she seems to be wrapped up in her work, and the second you broach the topic of a custom job she shuts you down, flat.
Not with the war on, she says. Captain Runcible has everybody going full-time to arm the militia. First you've heard of war. You might be able to finagle some permission out of the Captain, but it might be more important right now to chase down some information. What are you doing?
1. No, and. Hmm. I don't want them to get immediately violent, but what can I- ah! Show a downside to their class, race, or equipment.
You ask if he does custom work, Fightgar, and he grins and invites you around the counter - but as soon as you're clear of the display racks and he catches sight of your clan-braids his face goes hard. But not for you, he says. Get out. Stonehammer gold's no good here.
Oof. Your clan reputation's come into play before but never this hard. Can you think of anybody with that kind of grudge against the clan, Fightgar? Obviously he knows what's going on, but you get the feeling asking might just make it worse. What are you doing?