Creating a map that works with the Hostage Rescue gamemode is fairly simple. You need to define three entity types (CT Spawn, T Spawn, Hostage Spawns) plus two brush types (Hostage Rescue Zone and Buy Zones).

In this guide, I'll be working to convert gm_construct into a map for the hostage rescue gamemode.

Place Hostages

Use the info_hostage_spawn entity to place where hostages may spawn.

Hostages should ideally be spawned near where Terrorists spawn.

Rescue Zones

Similar to Buy Zones and Bomb Sites, create a brush with the tools/toolstrigger material and then press CTRL + T to tie it to an entity.

Select func_hostage_rescue.

Spawn Points & Buy Zones

The next step is to define where Counter-Terrorists and Terrorists spawn.

When you define spawn points, you'll also need to create another trigger entity for the buy zone.

Creating Spawn Points

We use the following entities for player spawning:

info_player_counterterrorist

info_player_terrorist

These are fairly obvious.

Use the entity tool to place a new entity; by default it will spawn info_player_start.

Double click on the entity to open the inspector and change it to either info_player_counterterrorist or info_player_terrorist.

Once you've created one spawn point, you can use the Hammer++ gizmos, dragging left or right while holding down the SHIFT key, to duplicate it.

Creating a Buy Zone

Similarly to creating a Bomb Zone, create a trigger brush that covers all of your spawn points.

Press CTRL + T to tie the brush to an entity and then set the entity class name to func_buyzone.

Press "Apply" and then set the Team Number to the team the buy zone is intended for; in this case it's CT.

Repeat these steps for the Terrorist spawns with info_player_terrorist.