First of all, see the previous question here about what backdooring actually is. Next, note that in Dota2, backdoor protection exists on everything except the outer ring of towers. From Liquipedia's Structures page:
Tier 2, 3 and 4 towers have backdoor protection, which causes them to regenerate at 90 hp per second and take 25% damage from illusions if they are attacked without nearby creeps. If there are enemy creeps or corpses nearby, backdoor protection is disabled. Backdoor protection will not regenerate damage dealt by friendly units.that Tier 1 towers don't have backdoor protection.
So in order to backdoor successfully, a building needs to be low enough to be destroyed in a single hit, or the hero needs to be able to sustain greater than 90 damage per second, after reductions due to armor and building type. This is generally very difficult for most heroes for most if not all of the game, with backdooring typically being a team effort or single-hit kills.
Things to look for in a backdooring hero:
- High DPS - To overwhelm the BD protection you will need a lot of damage and attack speed, late in game many heroes can do it but earlier it makes for a big problem.
- Mobility - You will have to get to their base quickly as possible and/or unseen to avoid enemy team defending.
- Summoned units - They can be good way of backdooring since you don't have to put yourself in danger, but rarely have enough damage without hero contribution.
- Items - Boots of Travel, Shadowblade, Necronomicon, Manta Style, Helm of the Dominator, Mask of Madness or just a lot of pure DPS items.
- Nature's Prophet - Teleport,spawn treants,DPS
- Lycanthrope - Very fast,DPS
- Lone Druid - Summoned bear deals a lot of damage to towers, DPS
- Leshrac - Diabolic Edict deals huge damage to buildings if no nearby units
- Clinkz - Fast invisibility, DPS
- Troll Warlord - Only crazy DPS
- Phantom Lancer - Lots and lots of illusions, invisibility, DPS
- Death Prophet - Fast, ghosts can destroy buildings quickly if no nearby units
- Broodmother - Partial fast invisibility, broodlings, DPS
- Meepo - Can simultaneously defend and backdoor as needed using poof, DPS
- Warlock - Powerful golems
- Faceless Void - Chronosphere, DPS
- Chaos Knight - Fast, strong illusions, DPS
- Tiny - Huge damage, +75% to buildings with scepter
- Visage - Gargoyles