There's a big national convention coming to town that will give Philadelphia a chance to show off what a spiffy, exciting place it has become. No, not the Democrats; it's the American Institute of Architects. Some 19,000 of those exacting design minds will be prowling our streets next week, taking measure of our stone citadels, peering at our construction sites, and generally giving us a professional once-over.

What will they make of the things we've built? The visiting architects will find Philadelphia is a very different city from the one they experienced in 2000, the last time the AIA held its convention here. (That also happens to be the year the city hosted its most recent presidential convention.) Back then, Philadelphia was just starting to pull itself out of a decades-long slump.

Today, a sizable chunk of central Philadelphia feels like a thrumming construction zone. (Watch your step, architects.) Three glass skyscrapers are rising on the Schuylkill waterfront, and thousands of new rowhouses are gobbling up empty lots, not to mention way too many 19th-century buildings. It's not only Center City that is thronged with pedestrians these days; the neighborhoods are as well. The surging restaurant scene and growing bicycle culture add to the bustle.

Philadelphia is by no means the only large city to experience a warp-speed comeback over the last 15 years. America is living through a historic period of urban reconstruction, at a level not seen since the early 20th century, when immigrants and industry were pouring in. That was a great era for architecture in Philadelphia.

The AIA members will find it's more of a good news/bad news story today. The city's institutional buildings - its universities, hospitals and museums - are becoming ever more deluxe and bespoke. High on the AIA's list of must-see sites are the Barnes Foundation and the glass outcrop of the Singh Center for Nanotechnology. Designed by celebrated out-of-town architects, they rank among the best new buildings in America.

But our everyday buildings, the ones where we spend most of our time and that shape our response to the city, aren't getting the same first-class architectural treatment. Those structures tend to be built by private development companies whose business is turning real estate into money - quickly. Some developers do produce memorable architecture, but they're the exception.

Of course, you'll find mediocre developer-driven architecture in every American city. What's different here is the numbing sameness of the designs, especially among the high-rises. University City's emerging skyline is largely made up of slab towers artlessly clad in asymmetrical arrangements of glass and solid panels. In place of carefully worked details, the designers simply pop in some colored panels to capture our attention. It's as though they were designing two-dimensional objects instead of buildings that are seen in the round.

One of the first buildings the visiting architects will encounter when they leave the Convention Center is Home2Suites at 12th and Arch, a design that could have been airlifted straight from a highway. The boxy mid-rise is encased in a wan, plastic-looking stucco, nearly devoid of refining details that bring a flat facade to life. The cheap facade makes for a sharp contrast with the neighboring Reading Terminal market, a stone heavyweight that was a technological marvel when it opened in 1893. Its glass barrel vault was the largest single-span structure in the world. Such innovation and ambition are virtually absent today.

Home2Suites epitomizes several architectural trends we're seeing in Philadelphia and other booming cities. As developers have scrambled to capture the growing urban market, they've abandoned traditional materials like brick and stone in favor of EIFS stucco, metal panels, cement board and glass. These products aren't necessarily cheaper, but you don't need the same level of skill to install them. That means buildings can go up faster.

Another factor working against good design is the way buildings are financed. In the days when developers held on to their buildings for decades, they had an incentive to invest in good craftsmanship and durable materials. Now, most apartment projects end up being flipped to big management companies, and developers want to spend as little money up front as possible. Philadelphia's high labor costs make even less money available for real architecture.

Philadelphia is suffering in particular from a scourge of metal-panel construction, like PMC Property's 1900 Arch St. The building is blanketed in an array of blue-gray matte panels, which absorb light like a black hole. The material produces an entirely different experience from the one you get looking at a masonry building. Even though we might describe bricks as "red," or "buff," they're actually a range of colors, contrasted by bands of mortar that add texture, shadow, and scale.

It's not that metal panels are inherently bad. They're actually very energy efficient. Used creatively, they can give a building a techy, modern feel. At Twelve/40, a new condo building at 13th and South, ISA's Brian Phillips wove silver panels into a rippling composition. One reason it works is that vertical seams and deeply set terraces give the facade texture and rhythm.

You could hear some of the frustration with the state of Philadelphia design expressed at several recent meetings of the Civic Design Review board. In April, Nancy Trainer - who worked alongside Denise Scott Brown and Robert Venturi, who will receive this year's AIA Gold Medal - begged the architects of Bart Blatstein's South Broad Street bulky high-rise to return to the drawing board.

It's not all bad news, though. Philadelphia architects have stopped trying to pass off faux historical buildings, like Symphony House, as the real thing. Designers and developers have begun to master the basics of good urbanism. Even Home2Suites, for all its faults, is ringed on the ground floor with big windows and a lively array of restaurants. If this boom keeps up, maybe Philadelphia developers will start to get the architecture right, too.