AOSP emulator support rich options, like screen size, memory size, specify img path, etc. Here's some examples:
1. Run emulator by specify partition, memory amd screen size

$emulator -partition-size 512 -memory 1024 -skin WVGA800 -verbose

2. Run emulator by specifying img files,including kernel

$emulator -sysdir out/target/product/generic/ -system out/target/product/generic/system.img -ramdisk out/target/product/generic/ramdisk.img -data out/target/product/generic/userdata.img -kernel prebuilt/android-arm/kernel/kernel-qemu -sdcard sdcard.img -skindir sdk/emulator/skins -skin WVGA800 -scale 0.7 -memory 512 -partition-size 1024

3. You can also create a AVD(Android Virtual Device) and us it with your emulator

$emulator -avd normandy_dev -kernel ./out/target/product/msm8625/kernel-qemu -verbose

4. Emulator Skins

The AOSP includes the following emulator skins: QVGA (240x320, low density, small screen) WQVGA400 (240x400, low density, normal screen) WQVGA432 (240x432, low density, normal screen) HVGA (320x480, medium density, normal screen) WVGA800 (480x800, high density, normal screen) WVGA854 (480x854 high density, normal screen) WXGA720 (1280x720, extra-high density, normal screen) WSVGA (1024x600, medium density, large screen) WXGA800-7in (1280x800, high density, large screen) new WXGA800 (1280x800, medium density, xlarge screen)

5. How to disable Soft-navigation bar from bottom of screen? Start your Emulator and do below steps...

$adb shell
$setprop qemu.hw.mainkeys 1 && stop && start