There are no rules for creating lower HD Constructs or altering the book ones except Modifications.
However, you could build them from the ground up using the rules for Building New Constructs. This section relies heavily on GM oversight for appropriate benefits, but references Monster Creation Rules as a baseline.
This is an example of what a 1HD Flesh Golem might look like. You will have to work with your GM, but based on 1HD and medium Construct HP, the CR should be at least 2. Following the Monster Creation Rules table for CR 2 (and comparing it to the CR9 Flesh Golem and how they interact with the table), you expect +4 to hit with its attacks and 14 AC. Most of the rest of it falls into place after adjusting its BAB to match it's HD and it's ability scores to reach these values.
Golem, Lesser Flesh
N Medium construct
Init –1; Senses darkvision 60 ft., low-light vision; Perception +0
AC 14, touch 8, flat-footed 20; (–1 Dex, +6 natural, –1 size)
hp 26 (1d10+20)
Fort +0, Ref +0, Will +0
DR 5/adamantine; Immune construct traits, magic
Speed 30 ft.
Melee 2 slams +4 (2d8+3)
Space 5 ft.; Reach 5 ft.
Special Attacks berserk
Str 16, Dex 9, Con —, Int —, Wis 11, Cha 1
Base Atk +1; CMB +14; CMD 14
When a flesh golem enters combat, there is a cumulative 1% chance each round that its elemental spirit breaks free and the golem goes berserk. The uncontrolled golem goes on a rampage, attacking the nearest living creature or smashing some object smaller than itself if no creature is within reach, then moving on to spread more destruction. The golem’s creator, if within 60 feet, can try to regain control by speaking firmly and persuasively to the golem, which requires a DC 19 Charisma check. It takes 1 minute of inactivity by the golem to reset the golem’s berserk chance to 0%.
A flesh golem is immune to any spell or spell-like ability that allows spell resistance. In addition, certain spells and effects function differently against the creature, as noted below.
- A magical attack that deals cold or fire damage slows a flesh golem (as the slow spell) for 2d6 rounds (no save).
- A magical attack that deals electricity damage breaks any slow effect on the golem and heals 1 point of damage for every 3 points of damage the attack would otherwise deal. If the amount of healing would cause the golem to exceed its full normal hit points, it gains any excess as temporary hit points. A flesh golem gets no saving throw against attacks that deal electricity damage.
Lesser Flesh Golem Construction
The pieces of a flesh golem must come from a normal humanoid corpse that has not decayed significantly. Assembly requires dismembering the body and reassembling it. In some cases, more bodies may be necessary. Special unguents and bindings worth 500 gp are also required. Note that creating a flesh golem requires casting a spell with the evil descriptor.