Crafting magic items takes one day for every 1,000 gold pieces of its value and spells have to be cast every day. Although it takes one day for every 1,000 gold pieces to craft a construct as well, I can find no mention that you have to cast the required spells every day.
Can I nonetheless assume that spells have to be cast every day to craft a construct?
RAW spells do not have to be cast every day while creating a construct
In Creating Magic Items it is specifically statet that spells have to be cast every day. Here is an example for armors:
The act of working on the armor triggers the prepared spells, making them unavailable for casting during each day of the armor’s creation.
Nothing of the kind is statet for crafting constructs:
The creature can create any construct whose prerequisites it meets. Enchanting a construct takes one day for each 1,000 gp in its market price. To enchant a construct, a spellcaster must spend 1/25 the item's price in XP and use up raw materials costing half of this price. The creature can repair constructs that have taken damage. In one day of work, the creature can repair up to 20 points of damage by expending 50 gp per point of damage repaired. A newly created construct has average hit points for its Hit Dice.
It also cannot be found in all the entries for different constructs in the MM and neither is it stated in the WotC Archive on crafting construct rules (although it is specifically stated again in the magic item creation entry).
The Monster Manual also states the following things:
Monster Manual p.134:
Creating a golem is essentially similar to creating any sort of magic item.
however it also states this:
Completing the golem’s creation drains the appropriate XP from the creator and requires casting any spells on the final day.
Monster Manual II p.115 states:
The real work of creation involves extended magical rituals requiring two months to complete. Understanding the rituals requires a character of the appropriate level with the Craft Magic Arms and Armor and Craft Wondrous Item feats.
This does not specifically say anything about casting the required spells. Also this specific part about the construction of Golems states that the spells have to be cast on the final day, just as the Monster Manual does.
The construction section on every Golem in Monster Manual II affirms this again. Consider this example of the Brass Golem (p.117).
Completion of the ritual drains 4,000 XP from the creator and requires the geas/quest, limited wish, maze, Mordekainen's sword and polymorph any object spell.
Thus this suggests that the spells only have to be cast at the end of the ritual rather than every day.
Pathfinder (although being a different rule system than RAW 3.5) specifically states that the spells have to be cast every day, although they can be omitted by raising the craft DC by 5:
The act of working on the construct expends the prepared spells, making them unavailable for casting during each day of the construct’s creation (that is, those spell slots are expended from the caster’s currently prepared spells, just as if they had been cast.) For each spell requirement you do not meet, the DC to craft the construct increases by 5.
