amfoto1 Loc: San Jose, Calif. USA

It would be kinda helpful to know what camera you are using.... pretty hard to recommend lenses without that info.

It also may help to know how you are using the shots (i.e., how high quality they need to be) and, unless money is no object, how much you've budgeted toward the purchase.

EDIT: Ah... I see you got back to let us know you're using a Nikon D7200.

In that case... if your budget is unlimited the best wide angle for the purpose would be a Nikon PC (perspective control) lens. Those are ideal for architectural work, since you can shift and tilt the lens to reduce perspective distortions. These are rather pricey and manual focus only. I think the widest Nikkor PC available is 19mm that costs about $3400. This superb FX lens would not be particularly wide on your DX camera.

Nikkor DX 10-24mm and 12-24mm are wider alternatives on your DX camera... But Nikon puts a high value on these lenses (which really aren't any better than some of the 3rd party lenses below): $900 and $1100 respectively.

But assuming your budget isn't unlimited, there are more affordable alternatives:

One interesting possibility might be the Laowa Venus 15mm Macro/Shift lens. At $500 it's far cheaper than, yet nicely wider than the widest Nikkor PC. This has a single axis movement similar to the Nikkor PC, making possible some perspective distortion correction (such as "keystoning"). However, this is a manual focus and manual aperture lens... and it's gotten mixed reviews for architectural/scenic uses (it's primarily intended as a macro lens capable of full 1:1).

And there are a host of 3rd party zooms:

Tokina 12-28mm f/4
Tokina 11-20mm f/2.8
Tokina 12-24mm f/4 (discontinued, used)
Tokina 11-16mm f/2.8 II (discontinued, used)
Sigma 10-20mm f/3.5 (clearance pricing?)
Sigma 10-20mm f/4.5-5.6 (discontinued, used)
Sigma 8-16mm (widest non-fisheye, but heavy distortions)
Tamron 10-24mm

Bolded lenses above are ones I've had chance to try out and compare personally, at one time or another, here listed somewhat in sequence of best to worst in my opinion, based on image quality, build quality, overall performance, etc. After trying out as many as I could at the time, I bought and used the Tokina 12-24mm for a number of years on my Canon cameras. More recently I've been using Canon's very good 10-22mm, which unfortunately isn't an option for use on Nikon cameras.

The Tokina 11-16mm f/2.8 is quite sharp, but it's also very prone to flare and has a very narrow range of focal lengths, in order to have the largest possible aperture. This now-discontinued lens is popular for astrophotography and journalism, where it's large aperture can be helpful. But a large aperture isn't typically much benefit for scenic or architectural photography... In fact most people stop their lenses down quite a bit for scenic or architectural shots, to get maximum depth of field and sharpness from near to far and/or use a tripod to allow for longer shutter speeds. Interior architectural photography also may use a lot of lighting gear, making a large aperture lens less necessary.

The Tokina 11-20mm and Sigma 10-20/3.5 are a bit larger and heavier than the other lenses. They both require larger 82mm filters, which can be considerably more expensive than the 77mm filters used by the rest of the lenses listed above.

I suspect Sigma will soon be announcing a replacement for their two models of 10-20mm (larger, more expensive one with f/3.5 aperture and smaller, more affordable with variable aperture). One is now hard to find new. The other is steeply discounted from it's original MSRP, I would guess to clear the shelves for something new that's in the works.

The Sigma 8-16mm is the widest ultrawide lens available that's not a fisheye lens. It has relatively heavy wide angle distortion and a convex front element that precludes using standard screw in filters on it. The strong distortion may present some problems for architectural photography, but an extra wide lens like this may be helpful for small interior spaces. This Siggy uses a shallow built-in fixed (permanent) lens hood, so it requires a special lens cap.

Tokina also makes a 10-17mm that's fisheye at it's widest settings. Again, fisheye have really strong distortions that can be problematic for architecture. This Toki also has a convex front element that precludes using standard screw-in filters and uses a special hood and lens cap.

The Sigma 12-24mm is not listed above because it's actually a full frame (FX) lens that typically costs a lot more with no added benefits for a DX camera user. In fact, it is also less well corrected than some of the other lenses listed. This Siggy is another lens that has a convex front element and built-in, fixed (permanent) lens hood, so requires a special lens cap.

Camera buyer Loc: Las Vegas

I use a Canon-16-35mm lens on my full frame Canon6D and 5DMkII. I use my camera in a tripod, using Live view. I shoot every thing in RAW.
I open shadows and correct any minor distortions in Photoshop "Skew". I don't use ANY supplementary lighting. I believe the shot should appear as it does in reality.

cjc2 Loc: Hellertown PA

For my Real Estate work, I normally use my D810 with a Nikon 14-24 or sometimes the 24-70. If I need wider than that, I might do a small panorama. Tripod, wireless release and the occasional HDR are also in my toolbox. And yes, I prefer to portray reality as well. Best of luck.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Since you are doing architectural and not real estate, you are looking for a natural perspective. An ultrawide lens won't give you that. Best solution is a tilt shift lens 24 and 45mm on full frame. Also, stitched panoramas are pretty common, which preserve a natural perspective using a medium focal length (without significant extension distortion).

cjc2 Loc: Hellertown PA

Good point Gene. I generally use the terms interchangeably, which is not correct. I am NOT an architectural photographer by any stretch of the imagination.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

The RE market will use photos that can be disingenuous about a room's depth. Ultra wide lenses excel at making a 20 ft deep room look like it's 40 ft deep. That would be unacceptable to most creative directors and architects, though there are exceptions.

cjc2 Loc: Hellertown PA

You'll be happy to know that is not my intent, but I find it unavoidable on some occasions. My goal is to give the viewer a look into the apartment or home without distorting it. I try hard to make images to attract interest, not oversell something that is not there. I've worked, on occasion, with others who produce images for architects for the experience, but the RE marketplace is just not willing to make those investments unless the home is expensive and impressive, at least where I am located.

Basil Loc: New Mexico

<delete> (I didn't see you had mentioned in later post what camera you were using)

TREBOR77 Loc: Winchester Kentucky

Thank you for your information...!

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

And you nailed the reasons I never do RE work. In the 70s I did a fair amount of work for architects, interior designers and developers, using large format cameras. It paid well enough to cover my tuition and living expenses while getting my degrees.