Cities and buildings come up a lot in questions. I'll put together a software specific tutorial on buildings, but today I'm just going to go through my philosophy when illustrating a featured building like a castle or a temple. The process is the same, regardless of software. In this case - ballpoint pen on sketchbook paper.
A map is a complex image. We want to be able to access the important information quickly. To do this we can use three things the human brain does very well - identify things that don't fit the pattern, notice detail and focus on contrast. By giving out featured buildings interesting shapes we break any pattern of regular rooftops, and by detail and tonal contrast, we help the eye focus on them amongst the sea of buildings.
1. Design the outline
Historically, the most likey shape for almost any building is a rectangle. But that's pretty boring on a map. How do you know that a building is special from overhead if they're all rectangles? Here I've drawn three outlines for three featured buildings.
The Inn has a main building, a stables and an outhouse/privy. The whole area is surrounded by a wall or fence, and the central area has a courtyard. The negative space (the courtyard) will stand out in a top down map.
Temples are fancy. They're meant to impress, and they're meant to dominate. This meand buttresses and spires. I've avoided anything that might look like a cross - as that's always going to break any sense of disbelief - but the same principles apply. Add off-shoots and extensions. If it's a lawful god, make the building symmetrical. If it's chaotic, make it a rambling sprawl, if it's militaristic, add towers and gates. Circular buildings and domes are a good choice here too, especially when using graphics tools that make perfect circles easy.
There's a lot to be written about castle design, so I'm not even going to try here. I've gone with a simple keep/fortified manor house and a curtain wall. Tower guard the vulnerable corners, and there's a hefty gate guarding the entrance.
2. Add Detail
Here we add some lines to give some sense of the detail. Our eyes are drawn to detail naturally, so if you add more detailing to your featured buildings, they'll stand out in a map. Here I've added lines to indicate thatching or tiles to the Inn. The temple also gets some tiles, as well as a turret or bell-tower at one end, and some little roof elements. The castle picks up walkways on the walls, detailing on the keep's roof and some internal buildings in the castle grounds (well, we all need somewhere to keep the foot soldiers, hawks and the horses).
So this is going to be different depending on the medium your using, but it's the point where the building stops being a flat sketch and starts to take on some life. Pick a direction for the light, and shade in blocks away from that direction. Note that buildings cast geometric shadows, and that shadows have different depths. The Inn gets simple geometric shadows, and a lighter shadow on the right side of the roofline. The temple i more complex - I use the shadows to emphasise the height of the tower, and the height of the buttresses. The castle gets the most work - each tower gets a long shadow, and I also added a set of battlements to indicate the crenelations on the walls. Deeper shadows here and there help to call out specific architectural features.
If you'd like to see these techniques in a finished map, check out my Iconic Town pack: [link]
More tutorials up on the blog: [link]